Transceivers communicate directly with the satellites using an antenna of roughly the same length as the handset and have a maximum output power of 2 Watts. QPSK modulation is used for the air interface. Thuraya SIM cards will work in regular GSM telephones and ordinary GSM SIM cards can be used on the satellite network as long as the SIM provider has a roaming agreement with Thuraya. As with all geosynchronous voice services a noticeable lag is present while making a call.