In an effort to boost subscriptions and advertise its unlimited data plan for the iPhone 4S, Sprint announced on Friday, May 18, that it will start offering a $100 credit to any customer willing to trade in an iPhone from another carrier.

"For a limited time, bring us an iPhone from any carrier and get at least $100 off a new iPhone 4S when you open a new line with Sprint or add a line to your account," Sprint said on its Web site. The offer applies to any iPhone model. A minimum two-year contract is required to start a line of service with Sprint.

Unlimited Data Plans

Sprint's announcement follows several reports earlier this week that Verizon Wireless would be planning to axe unlimited data usage for its smartphone users this summer, when the company rolls out its new shared data plans. Verizon issued a statement on Thursday, May 17, clarifying that this would affect only subscribers upgrading to a subsidized handset. It is only these subscribers who would no longer be able to benefit from the unlimited data plans.

Verizon's new upgrade policy, as well as AT&T's decision back in March to add speed caps for heavy data users after they exceed a 3GB per month threshold, were highly criticized. Both carriers have stirred great controversy for slowly pushing grandfathered customers out of their unlimited data plans.

Sprint is the last of the nation's three biggest carriers to offer the iPhone, and it announced its unlimited data plans to new customers just as AT&T and Verizon were announcing their decisions to end their respective uncapped services, turning to more lucrative tiered solutions. AT&T was the first to kill off unlimited iPhone data back in June 2010, and Verizon followed the same approach in June 2011, just six months after the iPhone launched on its network. AT&T CEO Randall Stephenson recently acknowledged that he wished the carrier had never offered this option.

Aggressive Competition

Meanwhile, Sprint stands out from the competition and CEO Dan Hesse announced in April that the carrier will keep offering unlimited data for the next-generation iPhone, yet to be announced. This means that Sprint customers will be able to utilize uncapped bandwidth even if the next-generation iPhone supports faster 4G LTE.

"Our competitors love to limit you to a measly 2GB of data usage. AT&T and Verizon give you unlimited text and talk, but they charge you extra after you reach that limit," reads Sprint's Web site if you hit the "learn more" button. "At Sprint, our Everything Data plans give you unlimited data, messages and calls to or from any U.S. mobile phone nationwide while on the Sprint Network."

Those interested in the offer must activate a new line with Sprint by July 3 and trade-in their iPhone from another carrier before August 14.