t for inter domain roaming and service continuity The future UMTS releases will have new and improved enabling mechanisms to offer services without using circuit switched network capabilities, as shown in Figure 9.3. Here, we assume that the set of services available to the user, and the quality of the ser- vices offered will match those available in networks that use CS enablers. Basic Services Multimedia Services Supplementary Services Operator Specific Services IP Multimedia Subsystem Packet Switched Domain External IP Networks Long-term UMTS Architecture Figure 9.3 Services in the forthcoming UMTS network architecture. The UMTS Network and Radio Access Technology 9.1.4 Classifying Releases 4 and 5 Services Following the suggested classification in [2], we can divide basic services into circuit tele-services [3] and bearer services [4], where both can utilize standardized supplemen- tary services [5]. These basic services have not changed much in 2G networks like GSM. GPRS [6] provides IP bearer services, and SMS, USSD and UUS can also be considered as a bearer service for some applications. IP multimedia services (including IP telephony) using GPRS as a bearer, correspond to the new services in R4 and R5. Supplementary services for IP multimedia services do not get standardized but they can get implemented using the toolkits or at the call con- trol level. Value added non-call related services (not necessarily standardized) correspond to a large variety of different operator specific services. These services may use proprietary protocols or standardized protocols outside 3GPP. To create or modify the above services (both call and non-call related services), service providers or operators may utilize standardized 3GPP toolkits (e.g. CAMEL or LCS) external solutions (e.g. IP toolkit mechanisms). Pre-payment can serve as an example of an application created with toolkits that may apply to all of the above service categories. Additional information and details on general and IP multimedia requirements can be foun