Sprint will join the iPhone carrier club, currently dominated by AT&T and Verizon, in October when the iPhone 5 is released -- and it will celebrate its entry by offering an unlimited data plan, a source told Bloomberg. If the information holds true, Sprint will be the only carrier in the U.S. offering an unlimited data plan for the iPhone. Both AT&T and Verizon had multiple data plans with varying prices and data quotas, but neither offers an all-you-can-use option. The move by Sprint is not too surprising;  the carrier already offers the same plan for $99.99 for other smartphones in its lineup, including Android and BlackBerry. A Good Deal -- But Only If You Use More Than 3GB per Month According to PCWorld's Tony Bradley, only heavy data customers who use more than 3GB per month can call Sprint's unlimited data plan a good deal, at least when gauged alongside AT&T's current rate. He figures that AT&T's 450-minute voice plan, priced at $40 monthly, is practically unlimited. "That 450 [minutes] comes with rollover minutes (carrying unused excess minutes over into a pool you can use the next month), 5,000 minutes dedicated to nights and weekends, and unlimited mobile-to-mobile calls," he wrote. "So, you may only have 450 'anytime' minutes, but if you are calling other mobile phones or making calls on nights and weekends, and carrying over extra minutes from one month to the next, the net result is essentially 'unlimited'." Throw in another $20 and you can send as many text messages as your fingers can sustain. So that brings together unlimited calls and text messages for $60, and comparing that to Sprint's unlimited data plan for $99.99, we're left with $39.99 for data. For that, we can buy a 2GB data plan with $25, and an extra GB for another $10. All in all, we're looking at what is essentially an unlimited call, text message and 3GB data plan for just $95. With the numerous cross-platform messengers available on smartphones like WhatsApp, Facebook Messenger and Apple's upcoming iMessages, you even have the option to save another $20 by dropping the unlimited messaging plan if you choose to use one of these services. Source: Bloomberg Photo credit: Steve Rhodes