Users can connect to an IMS network in various ways, all of which use the standard Internet Protocol (IP). Direct IMS terminals (such as mobile phones, PDAs and computers) can register directly on an IMS network, even when they are roaming in another network or country. Fixed access (e.g., DSL, cable modems, Ethernet), mobile access (e.g. W-CDMA, CDMA2000, GSM, GPRS) and wireless access (e.g. WLAN, WiMAX) are all supported. Other phone systems like plain old telephone service , H.323 and non IMS-compatible VoIP systems, are supported through gateways.
Martin Sauter hints at some of the services we can expect. His outline is very much focused on voice and business services.
Somewhat related to this is this article on the new Verizon service offerings.
At Experientia we have been doing some people-centred scenarios for a main telecom provider on the implications of this technology.
Though it is all covered by NDA, we do know that IMS is going to be big and that it will need much more subtle, refined and relevant user-centred scenarios than are currently available to make sure that all these investments make sense for people (and therefore for the businesses that reach out to them).