This was a hard one to figure out. My BB 8900 was working just fine on UMA in my home office today -- until sometime mid-afternoon (I'm in NJ, 35 miles south of NYC). Took me a while to see what was happening -- but it seemed that I lost the ability to get UMA reliably on my Blackberry.
In this location, the Blackberry normally gets a UMA connection over Wi-Fi to my Linksys WRTU54G-TM router, which was provided by T-Mobile for their @Home telephone service. This router also connects the handsets in the house to T-Mobile's network via UMA. Took me an hour on the phone with T-Mobile I it struck me that I lost UMA on both the 8900 and the @Home phone handsets at the same time. This was really odd, because the 8900 can generally get UMA over any old Wi-Fi router as long as ports 500 and 4500 aren't blocked.
My @Home router normally has a blue led indicator on when the SIM that's installed in it is properly registered on T-Mobile's network. The blue light had gone out. Normally, rebooting the router is the most that's needed to bring it back. Not working this time. So: blue light out, all home phones out.
Nagging in the back of my mind that there should be no connection between the blue light (and all home phones) going out and my 8900 losing UMA capabilities...but it became more and more apparent that these happened at almost exactly the same time.
So I get T-Mobile on the phone and walk them through the issues. The have me run a VoIP speed test through the router, and we see 69% QOS when it should be better than 85%. Not good. After an hour of futzing and testing, they make it clear that I have to work with Verizon to get the QOS fixed up, and then if the phone service doesn't come back they can troubleshoot more.
Just before calling Verizon, I decide to do some web searching for "verizon" mentions in the last hour. There it is -- Verizon had a major router failure in NYC this afternoon that went undetected for a while. An enormous amount of traffic was blocked. Even though they brought a new router back online by about 4pm, it seems that there were lingering network issues for the following 3 hours.
Quality of service on the Verizon line returned finally to 99%. UMA on my 8900 magically reappeared.
The blue light on my WRT54G-TM came back on and all the house phones started working again.
Still not positive what aspect of this blocked both the 8900 UMA connection and the T-Mobile@Home UMA service for my home phones. It could conceivably have been something blocking ports 500 and 4500 (UDP I think?), or perhaps it was the really bad quality of service at the time.
Here's a link to a Verizon blog describing the outage: Northeast Router Failure - Verizon Community
I can't have been the only one to lose this -- pretty bad situation -- for about 2 or 3 hours, there was no T-Mobile@Home service and no UMA possible with a Wi-Fi connected Blackberry (or any other UMA phone) if your ISP was Verizon in this region surrounding NYC...
Seems to be back now....