Is it possible to build a modem that hooks up with a 4G tower?

I can't get an ISP where I live but I'm seeing Sprints 4G modem can probably run xbox live games if they didn't cap me. So what if I designed my own modem and created my own bandwith(if possible)and just hooked into their tower and used my own bandwith so they couldn't get me for stealing. Is this possible? Is it legal? No BS answers like oh just get an ISP, if it were that easy I would.