ld justify its own service class for the network designer. Messaging offers user-to-user communication via storage units with a store-and-forward mailbox, and/or message handling, such as information editing, processing and conversion func- tions. See Section 5.3.6. 5.5 VALUE-ADDED SERVICES The meaning of the term value-added service (VAS) is not very clear. In Understanding Telecommunications, book 1, a distinction was proposed between IN and VAS services, where IN was network oriented and labelled advanced fundamental technical plans, and VAS was in principle implemented outside the network and more equal to information services. In any case VAS is interpreted as something more than ordinary telephony. The examples below show that service enablers play a key role for VAS. Service enablers are further described in Chapter 8. Let us take location as a VAS example. By using information about the subscriber that is available in the home location register (HLR) or mobile positioning centre (MPC) the information can be tailored to the subscriber position. The HLR knows the cell where the subscriber is located. The MPC can give even more exact positioning when equipped with GPS, and can also provide geo-navigational services. Messaging functions for MMS and other messaging services is another added value. Understanding Changing Telecommunications - Building a Successful Telecom Business Video playback can also be regarded as a value-added content service. For a business user who can access the same information from many devices a syn- chronization service is appreciated. Imagine a business user who owns a mobile phone, a PDA, a laptop computer, and a desktop PC. Assume that it is possible to perform an update to a contact's phone number stored on the mobile phone, and that this update would be transmitted to other devices and databases. This broad update could include a contact list on the PDA, a contact list within Outlook on the laptop and desktop PC, a corporate CRM database, and potentially an Internet-based calen