The issue with the above, is you need a dedicated SIM to go with the unit. Which means you'll be shelling out $10/mo to ATT or T-mob... and it needs power from the battery, which also means you're actively draining it...
I've tried finding something a few years ago with no luck.. What most of us are basically looking for is a 'bug' that is small and has a built in battery that would beacon its position few times a day/ once an hr to a server somewhere which could store the data for say a month..
No Luck!
They have the dog tags and baby tags.. but all require some kind of overnight recharging...
There was some research going on for implantable pet tags... Hopefully they don't get stuck on battling how safe the implants are for pets, so we here can keep our two wheeled pets safe!