An analyst with investment firm Citadel Securities said it was likely that Apple would deliver the iPhone to Sprint, the last carrier that still offers an unlimited wireless plan.

Citadel Securities analyst Shing Yin said it was unlikely that the two existing iPhone carriers, Verizon Wireless and AT&T, would try to stop Apple from adding the iPhone to Sprint’s repertoire. Sprint charges around $30 per month for an unlimited data plan, although some of its higher-tier plans include unlimited data as part of the package. Yin said it was likely that Sprint would get the iPhone sometime before Christmas.

Sprint is one of the last major wireless carriers still offering an all-you-can-eat wireless plan. Verizon will kill its own data plan on Thursday in favor of tiered plans ranging from $10 to $80 per month. AT&T killed its unlimited data plan last year amid complaints about its wireless network’s performance in large cities like New York and San Francisco, and now charges between $15 and $45 for tiered data plans each month.

The iPhone 4 currently retails at $199 for a 16-gigabyte model and $299 for a 32-gigabyte model, and both require a contract with wireless providers AT&T and Verizon. That puts the phones out of the price range of many devices that run Google’s operating system, Android, which can cost as little as $50. Apple currently sells an 8-gigabyte model of the iPhone 3GS, the phone manufacturer’s last generation phone, for $50 in order to hit that market point.

We’ll be exploring the most disruptive mobile trends at our fourth annual MobileBeat 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. We’re also accepting entries for our mobile startup competition at the show. MobileBeat is co-located with our GamesBeat 2011 conference this year. To register, click on this link. Sponsors can message us at sponsors@venturebeat.com.