Why We Care About UMA
Ted asks the musical question: should we care about UMA? Here is what, in my mind, makes UMA cool.
Makes Fixed-Mobile Convergence Possible: Not all office buildings have great mobile phone coverage. The odds of a mobile carrier addressing that with any sort of reasonable cost is nearly zero. By allowing GSM/CDMA/UMTS/HSDPA/whatever to be supplemented by WiFi, which business are already deploying and can be done so cheaper than GSM, et. al., you now have a phone that is capable of being used both inside and outside the office reliably. When you have that, FMC becomes at least feasible.
More Capacity For The Carriers: The carriers themselves see UMA as a way of increasing the amount of traffic they can serve on their network for practically no cost. Why wouldn't they want more capacity for free?
Seamless Handoffs are Needed: Let's face it, most people aren't technies like we are. The expectation of a mobile handset is that it "just works" and you don't have to "change modes of operation." The seamless handoffs that UMA will offer is needed to ensure that the end user just continues his call as before and not be any wiser that the layer 1/2 has changed. And for those of us in the know, it's a pretty amazing feat when it works.
Cheaper International Roaming: Imagine being able to use your GSM handset in a foreign country without having to pay astronomical roaming rates–provided you were in the range of WiFi. Takes the foreign GSM carriers out of the picture for at least some of the calls, making it possible to reduce or possibily eliminate international roaming charges.
There may be some other things that are cool about UMA, but those are the things that immediately come to mind.