Since 2007, Wi-Fi calling has been a major feature thats helped T-Mobile stand out from its larger carrier rivals in the US. Starting today, 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. On T-Mobile, the selection is far greater, though thats to be expected since the carrier has offered Wi-Fi calling for years now.