Originally Posted by jibi
Look at an evolution chart and think of IMS as 'man' and UMA as 'ape' - one is very complex and open-minded while the other is very simple and narrow-sighted
T-Mobile's adoption of UMA was a 'implement now' decision to give them an 'in-home' presence, as this was one key to what they lacked compared to all other major carriers in the United States. IMS is a fairly flexible technology that T-Mobile will likely implement on top of their UMA transport. As for time of implementation, from what I've read, it will start later this year (or it's already started) and continue through next year.
Good analogy jibi. Nice way to explain it. Tmo has already started implementing the layover IMS topology for their network. They are using our test equipment for it. Their issue was the IPv6 which was where they were lacking as far as gateway issues. In fixed networks, you have those gateways but since mobile was not really thought to go that route, its having to do "add-ons."
ATT is starting to as well, cept they are adding to their SIP stack to handle VOIP etc. They really are not fighting topologies, they compliment each other. UMA simply allows for the hand over for mobile devices to those features that IMS offers.
What will be interesting is to see the land line, cable carriers offers IMS packet services.