Unstructured Supplementary Service Data (USSD) is a technology unique to GSM. It is a capability built into the GSM standard for support of transmitting information over the signaling channels of the GSM network. USSD provides session-based communication, enabling a variety of applications.
USSD is defined within the GSM standard in the documents GSM 02.90 (USSD Stage 1) and GSM 03.90 (USSD Stage 2).
* USSD is instead session oriented, unlike SMS, which is a store-and-forward, transaction-oriented technology.
* Turnaround response times for interactive applications are shorter for USSD than SMS because of the session-based feature of USSD, and because it is NOT a store and forward service.
* Users do not need to access any particular phone menu to access services with USSD- they can enter the Unstructured Supplementary Services Data (USSD) command direct from the initial mobile phone screen.
* USSD commands are routed back to the home mobile network’s Home Location Register (HLR), allowing for the virtual home environment concept – the ability for services (based on USSD in this case) to work just as well and in exactly the same way when users are roaming.
* Unstructured Supplementary Services Data (USSD) works on all existing GSM mobile phones.
* Both SIM Application Toolkit and the Wireless Application Protocol support USSD.
If you is a subscriber of Operator Telecommunication, USSD is implemented on Credit Check like Telkomsel is *888# is application that build on USSD Protocol. Next Developmen USSD is on UMB – USSD Menu Browser. You can see on Next Thread.