I am a straight talk user for my phone and have purchased a DZ09 smart watch

[AC Question]

Will I have to buy a new sum are Can I use a old sim I already got

 

[B. Diddy]

Welcome to Android Central! Assuming your current SIM card fits (it has to be a microSIM size), it should work. According to this site, the watch supports GSM frequency bands 850/900/1800/1900 MHz, which should cover Straight Talk. DZ09 Single SIM Smart Watch Phone-11.99 Online Shopping| GearBest.com