Depending on several things there are basically two ways to go.
T-Mobile offers something I think they call a "hot Spot" not to be confused with what I"m using to send this post.. This is a "Micro-Cell" (Very small cell "Tower" actually a box that plugs into an internet Router (or Wi-Fi) and makes it a miniture cell tower. Short range. Might work for you or not)
And there are a couple of companies We-Boost and I think Max Signal that offer WIRELESS (Cellular) Range extenders...
These (We-Boost is the lesser of the two and can be found at many truck stops, it's also the less expensive and will LIKELY work if cell service is "Spotty")
THe system consists of an OUTDOOR antenna. and you have options including a DIRECTIOAL antenna (Good if you know where to point) and and indoor antenna.
And in between is a Digital Repeater Box..
NOTE.. Wi-Fi Ranger.. Same thign for Wi-Fi.. Just so you know.