With eBay’s acquisition of Zong Thursday for $240 million, it’s hard not see it as the first salvo in a major war over today’s most important business theatre, mobile payments.

It may not be a military battle, but the stakes are awesome nonetheless: $670 billion in mobile revenue is up for grabs by 2015, according to Jupiter Research.

Take a step back for some perspective. As far back as the late 1990s, business have been focused on the revolutionary potential of e-commerce. Once customers could shop online, it would be nothing short of complete rehaul of the way we did business, many thought. Bricks and motors would cede way to digital commerce: Pets.com, eToys and Webvan went public on the promise that they were the harbingers of the future.

But everyone overlooked something: The Web was awesome for researching information for shopping, but people still wanted to go to the store to actually check out — yes, touch and feel — the product they were buying. For some, it was the in-store experience. For others, a great deal of what they wanted — things like massages, travel excursions, or a great meal — could only be done offline anyway. So while only 7 percent of transactions were done online, 45 percent of transactions were researched online before an offline transaction was made.

What the smartphone has done, in the past few years, is allow shoppers to bring the Internet with them to the store, removing the last barrier to ubiquitous e-commerce. New mobile browsers, powered now by fast 4G/LTE networks, are helping. Whether the potential market is $670 billion, or slightly more or less, we don’t know exactly, but it’s going to be big. How big? Well, it’s the largest greenfield business opportunity available in the U.S. right now, period. Which explains the frenzy going on. More on that in a sec.

First, though, transaction infrastructure needs to be set up. How do you actually pay through your phone? Many stores and businesses have the point-of-sale  “readers” needed to accept payments via a credit card, like like you’ve seen in your neighborhood grocery store. A new technology called NFC, for near field communication, may make it even easier, through a wireless standard that lets merchant cash registers read payment data from your credit card or even from your smartphone.

Here’s what has braked the process until now: It costs a merchant up to $200 to upgrade their reader to incorporate this NFC technology. Merchants have balked, not seeing a reason to upgrade. But now, recognizing that NFC is the future, leading reader vendors like VeriFone are upgrading the readers with NFC directly, so that merchants don’t have to. Merchants still have to buy the new readers, which may still take years. But they have new incentives to do so: Keeping fickle, mobile customers loyal is more important than ever, and merchants can offer loyalty programs and other services much more effectively if they do so over the mobile phone (see Starbucks example).

While big merchants will be be the first to enjoy the new wave of NFC-based payment technology, the rest of the businesses — the vast majority that still don’t have readers — is still up for grabs.

Either way, there’s a massive scramble going on, by the major powers hoping to control the mobile app. Everyone wants to control the starting point, because that’s where they can force-feed customers information and offers — and thereby make even more money. We’ve written before about how NFC is going to be very, very big.

Many companies in the mobile payment space — in fact, most of them — will be represented at MobileBeat, our mobile technology event next week, where payment has become the central theme, and several companies are expected to make big announcements at the event. Here’s an overview of the biggest players.

Ebay/PayPal — Let’s start with this week’s instigator. EBay just acquired Zong, a company that allows you to pay for things via your cellphone bill. With Zong’s application, you simply give your cell phone number — either via SMS if you’re on your phone, or type it into a web page if you’re on a PC — and the retailer bills the charge to your carrier. It’s as simple as that.

EBay already owns PayPal, one of the leading ways you can make payments with mobile today. PayPal let you use an email address, and now with Zong it will let you use your phone number. Retailers on the other end now have more incentive to adopt Paypal/Zong in order to accept a bigger variety of payments — and they don’t otherwise need to change their behavior. This is potentially huge for Ebay. If it can have people start their purchasing with a PayPal mobile app, it can offer all kinds of other information about deals, including targeted offers.

PayPal’s senior director of Mobile, Laura Chambers, will be providing further updates on the company’s strategy next week at MobileBeat. Quietly, PayPal has emerged with an early lead: Eight million people use its mobile app, and they’re processing $3 billion a year in mobile transaction volume already.

Google Wallet — Google is the next antagonist in this war. Google recently announced its plans for Google Wallet, an app that lets you easily tie any of your credit cards to your phone and make payments to businesses that have installed NFC-enabled readers to accept credit cards.  It’s a bold move by Google to exploit its extremely popular Android phone operating system — Android powers more smart phones than any other OS — to get on your phone via its popular Google Market app store. Google wants Wallet to become the starting point, so that it can serve you a bunch of other offers (Google Offers).

But here’s where things are getting ugly. Google hired PayPal executive Stephanie Tilenius to help it run Wallet, and Tilenius in turn recruited employee Osmama Bedier to help. PayPal shot back with a lawsuit in May, claiming Tilenius had violated her contract with PayPal and stolen trade secrets from its mobile business. Tilenius is speaking at MobileBeat, but is unlikely to comment on the lawsuit.

How things unfold from here is unclear. Google aims to play nice on the technology level, but might have to play hardball to win this one. Google claims it is “open,”  in other words that is working with any credit card company and merchant, and won’t charge fees for using the Wallet service. It wants to make money, and attract users, by targeting consumers with Google Offers. The service debuts this summer, but it is limited in the number of places it can be used (and to start with, is only on the Nexus S phone), and will need to scale up quickly if it is to take off.

Still, it’s difficult to overstate the importance Google is placing on this. Jason Spero, head of Google’s mobile ad strategy, said Google is girding for “two massive macro cycles: the massive adoption of mobile computing (through smartphones), and then 18 month on the heels of that, mobile commerce.”

While there’s mad rush on by the big players to position themselves, almost everyone, including Google, says it’s still early. Some are downright skeptical that NFC will arrive in a big way anytime soon, and they cite the road-kill of past efforts. But just last year, while many insiders agreed it could be up to a decade before NFC-enabled mobile payments would become widespread. That has changed: Many people think it may be just a year or two away.

Groupon — As discussed above, targeting users with other offers on their phone is an obvious strategy for EBay and Google. But no one is benefiting right now more than the daily-deal site Goupon, when it comes to leveraging the Internet to allow offline, targeted commerce.

Some people have failed to appreciate the real driver of Groupon’s success. Here’s what’s driving it: The web is allowing millions of deal-seekers to come together to research these deals online, and then redeem what is effectively an offline good. These users take their Groupon deal and you redeem it at some store, restaurant or other place offline, thus bridging the decade-long gap between virtual deal-seeking and real-world fulfillment.

While Groupon first launched its mobile app in November, it’s already a top-50 app on the iPhone and it has 5 million users. The percentage of users adopting its mobile app is skyrocketing. Matt Murphy, venture capitalist of Kleiner Perkins, says more users will use Groupon via mobile than on the PC “before you know it.” Why? Because people increasingly are taking the Web with them while shopping.

While Groupon doesn’t have its own payment system, it’s become another starting place for mobile shopping — again a control point for where and how payments are made. And Groupon’s impressive success — it is the fastest company in history to hit a billion dollars in revenue, and its pending IPO may value it at up to $20 billion — is a huge warning bell for other players that they need to move fast.

Groupon is in a quiet period for the IPO, so is unable to speak freely right now. So we’ve invited LivingSocial VP Rich Kilmer to speak at MobileBeat next week. LivingSocial is the No. 2 deals company behind Groupon, and has arguably embraced mobile even more aggressively than Groupon. It launched its app a full year earlier than Groupon. We’ll also be hearing from Jeremy Stoppleman, CEO of Yelp, which has also just launched a local deal mobile program.

Square — It’s more than the mobile transaction, stupid! It’s the experience. That’s the message for Square, the shiny, cool new app founded by Jack Dorsey, the founder of Twitter. Within just two years of launching, Square valued at more than $1 billion. Square’s offering is at once elegantly simple, and incredibly complex.

Its offering begins on the simple side: A device that retailers and other small businesses can attach to their phones in order to accept regular credit card payments. But the back end is surprisingly sophisticated, comprising analytics, customer management, point-of-sale software and other tools for merchants to use, in addition to Square’s own fraud detection and security measures.

Like Dorsey, Square’s COO Keith Rabois has an enviable track record for helping create big brands: He was an early player at companies like PayPal, LinkedIn and Slide. Now the two are going for broke, aiming to build Square into a global brand by focusing on the user experience. In its latest offering, Square Card Case, Square can help merchants recognize customers automatically so that customers don’t even have to take out their credit cards to make payments.

Square is also allowing merchants to start their businesses on an Apple iPad, and offers them a dashboard to easily track transactions and everything else via the tablet. From there, Square hopes to upend everything from processing, point of sale devices, loyalty programs, receipts and analytics. In other words, Square hopes to be the starting point — a common refrain in this battle for payments. The big challenge for Square: Verifone, a publicly traded competitor, is already established as a reader technology at many large stores. Rabois will also be speaking at MobileBeat next week.

Visa (plus Mastercard, Discover, American Express and other credit card companies) — These card companies already control a huge portion of commerce, and so they’re fighting to maintain that control. They have little interest in disrupting the system. They’re more interested in ensuring cards can be used where they are now, and also extending into areas where they may not be used now.

PayPal, Google, Groupon and Square aren’t big threats, because they are complementary to cards (most of them tie their apps to a user’s credit card.) On the contrary, some credit card companies are investing in or allying with some of these efforts. They’re embracing all forms of NFC, even voice-enabled NFC.  Mastercard has backed Google Wallet, while Visa and American Express have launched their own “wallet” products, and are allowing these to be licensed by third parties.

In addition, Visa bought virtual good payments company Playspan for $190M in February. Visa has also invested in Square. American Express invested in Payfone, which allows mobile payments to be made with a mobile phone number (much like Zong), and has allied with Foursquare to power deals in check-ins.

Meantime, most of the card companies are backing ISIS, a loose alliance that is backing the NFC technology to allow cards to be used with phones.  As smug as this sounds for the credit card companies, it’s difficult not see signs of intense jockeying. There were early reports Visa would partner with Apple’s new iPhone 5, but then Visa announced its wallet product, and there was no announcement from Apple either, leading some to wonder what exactly Visa’s strategy is. Visa would not comment for this story, and Visa’s head of mobile Bill Gajda was on vacation at the time of this writing. But he’ll be back next week and speaking at MobileBeat next week.

Verizon, AT&T (and the rest of the carriers) — The carriers are the other major protagonists in this drama. For decades, they controlled the “deck” of phones here in the United States, but Apple’s launch of a phone with an independent App Store allowed developers and other publishers to do an end-run around the carriers and access users directly. Now carriers are struggling to regain control.

Of course, they have a big weapon in their arsenal: the phone bill. Carriers have supported the array of start-ups — Zong, Payfone, Boku, etc., that allow users to buy things using their mobile phone numbers and have this billed straight to their carriers’ bills. Still, that relationship with the customers is growing more tenuous by the day.

Meantime, Apple controls the payment mechanism on the iPhone’s popular App Store, through iTunes. Apple hasn’t really articulated a strong alternative mobile payments strategy for off-phone goods (though Square has partnered big time with Apple to support the iPad for small businesses). Now, Verizon wants to let customers use their phones for an array of things related to loyalty programs, and has openly embraced NFC. We’ll be hearing more from Verizon’s Humphrey Chen at MobileBeat next week.

The manufacturers — The final group of actors vying for control are the phone manufacturers themselves. And their efforts are centered on where the actual phone-secured payment information is stored and accessed. Basically, there’s fight to control the master app that oversees this and overrides all other payment functions.

For example, Google wants to allow a chip company, NXP, to be the vault for storing credit card information on the phone. Indeed, Google Wallet uses NXP on its Nexus S phones, and for now Samsung is playing along with this. However, the carriers want the secure element to reside on a SIM card, which they control, and here too, manufacturers are playing along in some cases. The manufacturers (Samsung, HTC, Nokia, Motorola), are stuck, often having to bow to demands from more powerful players in the chain, but ideally they’d want the info to be stored in embedded areas of the phone they control. However, competition is ruthless, and manufacturers seem to be fighting a losing war.

In sum, the spoils up for grabs in this mobile commerce war, are huge. The players who grab the customer first are most likely to win. Google is behind, but with its huge user-base, it will try to force users with aggressive cross-marketing, to adopt its app. PayPal is an earlyleader, as is moving quickly with EBay to exploit that lead. A horde of other players are jostling too, with Apple and Facebook yet to fully articulate their coming strategies. Amazon, BestBuy and other large retailers are also awakening to the trend. We think it’s the biggest opportunity for entrepreneurs and disruption today, which is why we’ve made payments the biggest focus of our upcoming MobileBeat event. The great news is, we’re seeing only the earliest battles of the war, and it will take several more years to play out. There’s time to get in the mud and fight. This will be one exciting show.

We’ll be exploring the most disruptive mobile trends at our fourth annualMobileBeat 2011 conference, on July 12-13 at the Palace Hotel in San Francisco. It will focus on the rise of 4G and how it delivers the promise of true mobile computing. MobileBeat is co-located with our GamesBeat 2011 conference this year. To register, click on this link.