Just a follow up on my UMA problems. I haven't heard back from T-Moible yet.
However, yesterday, I again rebooted my router and have had UMA ever since. I have no idea why when I first rebooted it, it didn't work, but it does now.
So, my suggestion for anyone with UMA problems on their personal home network, is to reboot everything more than once, if after the first reboot, it's still not working.