Keep in mind that if you travel not all areas have that service. It depends on who you get you cell service from and what level of service they offer where you happen to need it.
To illustrate where I live AT&T only offers 2G service (Edge) and there is an area about 25 miles from me that I do go to that they have NO SERVICE at all.
I have not kept up as well with T-Mobile and Sprint coverage here. I do know that they have some. But . . . the main provider in this area has been Verizon. They have extensive 3G coverage and are adding 4G. So, most in this area are with Verizon or a MVNO, such as Page Plus, that uses Verizon's towers.