I figured the trip to South Africa would be a good test of UMA calling on the blackberry in an international setting. I set up a wireless network connected to a DSL 256/512 connection. As soon as I connected to the WiFI network with the blackberry the UMA symbol popped up.
I disabled the carrier wireless network just to be certain that I would not be roaming and made a few test calls on UMA. The call quality was surprisingly good. I made a few changes enabling Quality of Service for the UMA ports – TCP 500 and 4500. I selected this ports per this RIM document
I am not sure if the QOS settings will make a difference or not.
Since South Africa is currently 7 hours ahead of the US, internet speeds are decent when the US is asleep. As soon as the US wakes up, the internet speed slows down significantly. The UMA voice quality also degrades when US internet usage begins in the morning US hours.
So far I am very satisfied with the service. I did make a mistake and pay the $9.99 with T-Mobile for UMA / WiFi calling when I did not need to. I am on the unlimited voice plan so using UMA voice has no affect on my minutes used. The $9.99 add-on is only for people with restricted minute plans, who want to use UMA / WiFi calling without burning the minutes on their plan.