Found this thread while trying to learn about UMA by searching on line.
I have a 8900 on Orange.
There was no sign of UMA appearing on my phone until I bought a new battery, it was completely dead when I purchased it so charging it in my phone resulted in about 4 fairly quick battery pulls ( i needed the phone unexpectedly
After the battery pulls UMA appeared on the phone ...... this may have been just co-incidence.
I have a Belkin router on BT broadband both at home and at work.
For one week I was connected via UMA at work with no problems then as of today no sign of it.
At home occasionally I get connected via UMA but it is very intermittant. A pain as that is where I need it, GPRS reception is patchy to say the least.
This seems to suggest to me that this has nothing to do with router settings or phone settings but is down to Orange as all my settings are constant but UMA comes and goes!