How can I find out if a phone is locked or unlocked?
First, I'm from the CDMA world, so I don't know much about GSM. But somebody gave me a used AT&T postpaid phone that I will activate on one of the AT&T MVNOs and give to a client. In order to do that it has be be unlocked, right? The phone powers up so the battery is good. I get the message Insert SIM. How do I determine if it is locked or unlocked?
In most cases, you need to insert a SIM card assigned to a different carrier (MCC / MNC). You would then be asked for the unlock code. A locked AT&T phone should work on most AT&T MVNO's as they commonly use the same MCC and MNC.
AT&T and most MVNO's are MCC=310 MNC=410
T-Mobile and most MVNO's are MCC=310 MNC=260
Lyca is MCC=311 MNC=96 and works by roaming on T-Mobile