SIP is an easy tool to do a variety of things. That is why it caught on in areas like wireless. Carriers have purchased licenses for 3G, and providers are already beginning to plan rollouts of networks, largely in Europe. And it's all going to be SIP in all 3G wireless handsets. It is not true that a SIP network requires that all services be in the phone.
Intelligence can be anywhere in the network.
One of the great things about SIP is that it is flexible. One result, though it was not designed this way, is that you can build networks with very smart cores, where most features and services live inside the network. In fact, you can put features in many different places. There is a strong movement in the industry to place a lot of features in devices called application servers that reside in the network and are not part of a softswitch. Our view is that a softswitch is a great access device to the public network, and what it does really well is provide large-scale SS7 connectivity to the telephone network.