What is GSM?
A key differentiator versus other 2G systems such as TDMA and CDMA is that GSM based systems include a Subscriber Identity Module (SIM), a smart card CPU that provides a globally unique subscriber ID allowing international roaming in 150+ countries.
Many GSM-based 2G and 2.5G handsets (mobile phones) also include a J2ME implementation, and as such are an important target for J2ME developers.
Many GSM SIMs implement the JavaCard technologies. For more information on JavaCard and its use in GSM SIMs, please refer to the jGuru JavaCard FAQ.