The SIM card provides a phone number that identifies your device on the carrier's network, whether it's T-Mobile, Verizon, or AT&T. It also ensures ... The lock is a PIN, which must be entered ...

[Jason Gin] wanted to reuse the SIM card that came with a ZTE WF721 wireless terminal he got from AT&T, but as he expected ... has no function to change the PIN and none of the defaults he ...