GigaOm confirms T-Mobile will add free Wi-Fi calls to its UMA-capable phones: T-Mobile tried an alternative to femtocell and unlimited calling plans several years ago, allowing unlimited domestic calls over Wi-Fi for handsets with unlicensed mobile access (UMA) technology built in. UMA allows seamless roaming between Wi-Fi networks and the cell network, handling the billing and call details on the back end. After a few years, however, even after making the add-on price as low as $10/mo for a family plan for unlimited calls that started on Wi-Fi (either placed or received on a Wi-Fi network at home or a hotspot), T-Mobile stopped offering the service to new customers. Apparently, it continued to be available as a calling option, with Wi-Fi calls being deducted from general minute pools. Now, T-Mobile is making Wi-Fi calling free to postpaid Even More and Even More Plus customers (those that have had a credit check and pay at the end of a billing cycle).…