Sprint may become the second major US carrier to let its customers make phone calls over Wi-Fi. According to Android Central, Sprint appears to be planning to support Wi-Fi calling on two existing Samsung smartphones and for all new devices running Android 4.2 or higher going forward. For customers short on voice minutes, that could be a big advantage as the calls won't count against their total. Phones won't be able to transition from a Wi-Fi call to a cellular call though, so leaving Wi-Fi coverage in the middle of a conversation would leave you with a dead line.

A small launch, with plenty of devices to come

There's no word on when the service will be announced, but Android Central has received training materials that Sprint is allegedly distributing in preparation for launch. The materials show that text messages can also be sent and received over Wi-Fi, though they don't mention if messages will count toward a service cap. Sprint's launch will reportedly be a small one though with just two minor devices supported at first, Samsung's Galaxy S4 mini and Galaxy Mega.

Sprint's support of Wi-Fi calling would come several years after T-Mobile first enabled the service. Though it was small there at first too, it's now supported by most major smartphones that it offers. With T-Mobile's aggressive new tactics now putting more and more pressure on Sprint to stand out, the carrier may feel that it's finally time to catch up where it can.