T-Mobile has done a fair amount to get LTE into every nook and cranny of its coverage map, but that doesn't matter much if there's still a cellular dead zone in your home or office. You might not have that issue from now on, though. The Magenta network is launching a 4G LTE CellSpot that promises full-fledged LTE calling and data -- you're not making do with 3G here. You only need an LTE-capable phone and a broadband internet connection to fill in those gaps.