The Wall Street Journal reports today that Virgin Mobile (owned by Sprint) will become the second carrier to offer the iPhone in the US on a prepaid plan. Cricket became the first to do so when it announced that it would start selling the iPhone 4S and 4 off-contract, beginning on June 22nd. Apple and Virgin have yet to confirm the news, but the WSJ says that the iPhone will be available on the carrier "as soon as" July 1st, citing "people familiar with the company's plans."

It's not yet clear whether Virgin Mobile will be selling the iPhone 4, iPhone 4S, or some combination of the two, and there's no information yet on how much the devices will cost off contract. Cricket said it would sell the 16GB iPhone 4S for $499.99 without a contract — significantly less than what it costs to buy the device outright from Apple. Of course, just like Cricket, Virgin Mobile runs on CDMA networks, making it difficult to use the device on any other carrier. The Wall Street Journal speculates that Sprint may be using Virgin Mobile (and perhaps Boost, which it also owns) to help sell enough iPhones to fulfill the up to $15.5 billion the carrier promised to Apple, which certainly seems reasonable considering CEO Dan Hesse's insistance that "carrying the iPhone will be quite profitable." It's not yet known if Virgin Mobile's current plans will be offered with the iPhone, but for reference, the carrier has a $35 per month plan with 300 minutes of talk time, unlimited text messages, and unlimited data. We'll let you know if we hear more to confirm the WSJ report.