The mobile station is the handset or mobile phone, but that is only a part of the complete mobile station. The handset is officially called the terminal, or mobile equipment. Originally it was available in handheld, transportable (bag phone), and vehicle-mounted versions. A handheld terminal radiated 0.8 watts of power while a vehicle-mounted phone radiated 20 watts of power. Transportable units lived in the 2-8 watt region. The rule of thumb was simple: the closer the user to the antenna, the lower the effective radiated power.
Perhaps the most important part of the mobile equipment is the subscriber identity module (SIM), which is often called the smart card or the smart chip as a means to make it more than it is. The SIM contains the personality of the user manifest in the wireless services the user subscribes to. More importantly, the services and identity defined on the SIM are not related to the handset itself. This means that the SIM card can be placed in any GSM phone since a GSM phone without a SIM is an empty mobile handset.