Read everything here and appears TMobile woukd be good option BUT maybe not. Here is issue....parents heading down in Dec. They have owned in Ajijic for years. Mom has short term memory loss. Have been looking at multiple gps tracker watches with little tech support defining coverage once in Ajijic. Put 2 +2 together....thought purchasing the TMobile Timex watch with tracker etc would be the answer BUT not one sakes person or tech can confirm it will work once they arrive, without an issue....sim switch etc. And from what I've learned so far sim card change oits i these type trackers is not easy. Contacted a friend in US who lives here but has family in Guadalajara. He tells me ATT all over Mexico now and his whole family on US contract. They have never had any issue with cell service while traveling throughout Mexico and they do not need any SIM changes to do so. I did find an ATT stire near Ajijiic which allows for support if something were to happen while they were down.....can anyone help here? Am looking to confirn a service with a watch that offers GPS tracking with perimeter boundary alarms, SOS call ability, and pinpoint tracking app that can be accessed both in USA and Ajijjic. The Iwatch is interesting but may be overwhelming for Mom. Just looking fir something simple and small.