This is a fully-functional SIM for public networks ... Everyone at Electromagnetic Field 2018 gets one of these GSM phone badges. Read Hackaday’s first look at the hardware.

A multi-carrier GSM phone with two, three or four SIM cards. Dual-SIM phones are popular with global travelers who use local and foreign carriers as well as people who want a business and personal ...

(Subscriber Identity Module lock) A function in GSM cellphones that restricts the phone's use to a particular cellular carrier identified by a SIM card. SIM locks are used to ensure subscribers ...

GSM phones can be "locked", that is made to accept only SIM cards belonging to a specific network. Typically, this is done so that phones will work only on the network of the carrier. SIM-locked ...