As nice as Google's Project Fi service is for the data-hungry crowd, it's not so hot for voice -- switching to Fi frequently means giving up pristine-sounding LTE voice calls with some of your friends. You might not have to make that sacrifice for much longer, thankfully. Google tells subscribers that it's testing voice over LTE with a "subset" of its customer base. This is likely only going to function when you're on T-Mobile's network (it's the only one of Fi's three partners with VoLTE as of this writing). However, you'll definitely know when it kicks in between the improved quality, faster mid-call data speeds and a quicker connection time.