Hi @fish2018 ,

According to the info from this link the GZDL watch uses a micro SIM card. The caveat is that the watch only supports the 2G network, so you need to get a micro SIM from a network provider that still has a 2G phone network in place. It will not work on the 3G/4G/LTE networks of any service provider

This is from the link above:

Phone Function: Can Be As A Standalone Mobile Phone To Make Phone Calls Including Answering And Dial-Up. Supports Single SIM Card (Micro SIM Card), 2G GSM/GPRS 850/900/1800/1900