Since 2007, Wi-Fi calling has been a major feature that’s helped T-Mobile stand out from its larger carrier rivals in the US. Starting Friday, however, Sprint will be offering the convenient perk to subscribers nationwide. Wi-Fi calling is completely free and allows Sprint customers to make voice calls and send texts over any Wi-Fi network. It’s a huge help when your reception is less than stellar at home or in the office. But in terms of device selection, your options are severely limited — at least for now. At launch, only the Samsung Galaxy S4 Mini and Galaxy Mega support the feature. On T-Mobile, the selection is far greater, though that’s to be expected since the carrier has offered Wi-Fi calling for years now. If you own one of those two devices on Sprint, you’ll need to download a software update before placing calls and sending SMS messages over Wi-Fi.