It was barely a month ago when we first heard rumors that Sprint might soon jump aboard the Wi-Fi calling trend, and that day has finally arrived - but only for owners of two less popular Samsung smartphones.

Sprint announced the launch of Wi-Fi Calling, a free service that allows subscribers to use existing wireless networks in place of the carrier's own.

The new service is intended to improve voice, data and messaging features in areas where Sprint coverage is limited or entirely absent, allowing unlimited domestic voice calls and messaging.

Wi-Fi Calling enhances Sprint's own coverage in existing homes, offices and public areas where a wireless network is available, but it won't do much for international calls or text messages, which will still be routed through standard CDMA service at the usual rates.

Mega or mini

Unfortunately for Sprint customers, Wi-Fi Calling is getting off to something of a slow start, with only two smartphones compatible at launch - and both of those are from Samsung.

Owners of the Samsung Galaxy Mega and Samsung Galaxy S4 Mini will be offered an over-the-air update "during the next few weeks" that enables the Wi-Fi Calling feature on their handsets.

After installation, the new feature can be activated by tapping the Wi-Fi Calling icon, which is located alongside other apps already installed on the device.

But there's hope for the rest of Sprint's customer base: The carrier plans to expand Wi-Fi Calling to "additional devices" throughout the year.