Since the announcement yesterday that Japan-based Softbank is making a bid for majority control of Sprint-Nextel, the analysts have been busy churning through the implications. But the simplest and clearest one is this: The US wireless market will no longer be a tightly-controlled duopoly. What’s even better, Softbank has the ambition, experience and sheer chutzpah to be what this market has always pined for but never had – a challenger who will shake things up. Consumers- cue the rejoicing.

Sprint has tried (sometimes admirably, often pathetically) to be that #3 player that made a difference, but even with last year’s company-busting iPhone bet, they just never had the capital they needed to be a proper player. Their purchase of Nextel was a bust (now they are finally turning off Nextel’s iDEN push-to-talk network, and all those construction guys are on other networks). Their embrace of all things WiMAX, including Clearwire, was doomed from the start. Their market cap is lower than their commitment to Apple to guarantee all those iPhones get sold, and Clearwire’s only decent asset is all that spectrum.

So now on to Softbank. You may know of them as a Japanese dot-com investor from the old days, and you would not be mistaken. They have spun off an impressive list of VC alums and spin-offs: Softbank Capital, which begat Mobius, which begat Foundry Group, Qiming Ventures, and many others. Brad Feld, Heidi Roizen, Gary Rieschel – what a list. You may also know them as major investors in Yahoo Japan (which has always been far more successful than its parent), and Renren, the ‘Chinese Facebook’. But you may not be familiar with how they came onto the telecoms scene in Japan and beat up the two incumbents.

In 2006, Softbank bought Vodafone Japan, formerly Japan Telecom, which was the struggling #3 wireless carrier (sound familiar yet?). In 2008, Softbank became the sole carrier in Japan to sell the iPhone, and they used their exclusivity to effectively double their market share (until KDDI finally got the 4S this year). NTT DoCoMo and KDDI were floored – unlike every other market on the planet, virtually every phone on their networks was from a local handset manufacturer (no Nokia, no Blackberry, no Motorola). Ten years ago, that meant Japan had the latest and coolest mobile technology; now it’s as woefully dated as, well, Nokia, Blackberry and Motorola! So the impact of the iPhone was earth-shattering: every time I am in Tokyo I am amazed by the number of people on the street lovingly staring at their iPhones.

OK, big deal, you say. Verizon, AT&T and Sprint all have iPhones now. But what Sprint doesn’t have is cash. Verizon and AT&T are flush with both cash and spectrum. An injection from Softbank would allow Sprint to finally take over the rest of Clearwire, and continue its plan to redeploy its TDD spectrum away from WiMAX to LTE. But in addition, Softbank can also help Sprint with its experience in marketing. It’s not clear if their omnipresent and hilarious mascot Otosan (‘Dad’ is a white dog with a human family) will make the trek across the Pacific, but it sure beats listening to Dan Hesse.

Otosan vs. Tommy Lee (aka ‘Alien’) Jones

Otosan gets his iPhone

T-Mobile’s grab at MetroPCS will help it gain some market share as well, but for now my bets are on Softbank/Sprint to bring some genuine mass market competition to the US mobile industry. And if they are even moderately successful, they may someday snap up T-Mobile too . . .

Paul Grim is a founder and General Partner at venture capital firm SunBridge Partners. Grim blogs on wireless issues at Grim Times.