I\'ve started my degree project, a mobile application suitable for iPhone, Android and (in the near future) Symbian. The server architecture is the following:
SOAP is simply too heavy for mobile communications. Why do all the work to wrap requests in an additional XML layer you'll have to parse? You send more data than you need to, and impose greater CPU burden on client and server.
Use REST. If you are doing a cross-platform project JSON makes a great payload container, otherwise plists work well for sending data from the server.