154GlossaryTo help you understand the main technical termsand abbreviations used in this booklet and take fulladvantage of the features on your mobile phone,here are a few definitions.Active FlipAbility to answer a call simply by opening thephone.Call ForwardingAbility to reroute calls to another number.Call HoldingAbility to put one call on standby while answering ormaking another call; you can then switch betweenthe two calls, as required.Call WaitingAbility to inform users that they have an incomingcall when engaged on another call.EMS (Enhanced Message Service)An adaptation of the Short Message Service (SMS)that allows users to send and receive ring tones andoperator logos, as well as combinations of simplemedia to and from EMS-compliant handsets.Because EMS is based on SMS, it can use SMScentres the same way that SMS does. EMS workson all Global System for Mobile communications(GSM) networks. EMS senders can use text,melodies, pictures, sounds, and animations toenhance the expressive power of messages that arelimited by the display constraints of mobile devices.Glossary155GSM (Global System for MobileCommunication)International standard for cellular communication,guaranteeing compatibility between the variousnetwork operators. GSM covers most Europeancountries and many other parts of the world.Line Identification Services (Caller ID)Services allowing subscribers to view or block thetelephone numbers of callers.MMS (Multimedia Message Service)A message service for the mobile environment,standardized by the WAP Forum and the 3rdGeneration Partnership Program (3GPP). For phoneusers, MMS is similar to Short Message Service(SMS)-it provides automatic, immediate delivery ofuser-created content from phone to phone. Themessage addressing used is primarily phonenumbers, thus the traffic goes from phone tophone. MMS also provides support for e-mailaddressing, so that messages can also be sent bye-mail. In addition to the text content of SMS, MMSmessages can contain still images, voice or audioclips, and later also video clips and presentationinformation.Multiparty CallingAbility to establish a conference call involving up tofive additional parties.