I have one of these in my AT Evo.
I used a step down converter and took power from my bypassed BMS. I used a text only plan from US Mobile ($4 a month) but I let it run out, and if I ever need to use it I can just pay the 4 bucks and start tracking it again. Works very well in my rural environment.
I ended up putting a switch on the power line tho as it will drain the battery in 1-2 weeks and it dosnt need to be on 24/7
I got this sim starter kit:
It looks like they lowered their price for texting only to $1.50 a month plus a couple dollars in fees.
I also took it out of the plastic case and wrapped it in shrink wrap. It is installed right under my BMS and together they are the height of an 18650 so it worked out perfect. If i get the unity beta 2 to test I will take some pics for you guys (and maybe post a build thread, wait who has time for that lol).