f there is no answer at the first device, it can proceed to ring all of the devices. 8.3.1.2 Enhanced Call Control It is possible to enhance the normal call barring or call forwarding services through the use of location or presence data. If the end user sets his presence to "busy," then all incoming calls could be barred or forwarded to his voice mail. Depending on the end user's location, certain calls could be handled differently. For example, if the end user's location is currently set to "Home," then calls from work related numbers could be sent to voice mail and he could instead receive an email notifica- tion of the call (with a text transcription of the voice mail message). 8.3.1.3 Rich Media Content Distribution Goveas et al. [11] suggest a blended service where the end user receives a combina- tion of offers depending on the end user's location and device capabilities. If the user's device is capable of receiving a multimedia stream, they receive a trailer for the latest movie release. If they are not capable of receiving the media stream, they can receive a poster for the movie instead. A virtual discount coupon can be sent to the end user if their location indicates that they are near a movie theater [11]. 8.3.2 Service Conflict Detection and Resolution The two main problems encountered in designing a system to handle service orches- tration is detecting the various interactions between services, as well as resolving any conflicts that arise. A system needs to be put into place that can determine when services are in conflict. Conflict resolution that takes place before the services are invoked is known as offline service resolution, whereas conflict resolution that happens during run time is known as online service resolution. An offline service resolution requires knowledge of all possible service interactions that can occur, and can be handled in several different ways. A popular approach is to build acyclic graphs or state tables indicating all the possible state changes/service flows that can occ