After the recent notification from TMO, I have yet gotten extra charges for international call via UMA. The calls were made from India and Thailand to US numbers.
This does not mean that it is 100% safe to say that TMO cannot figure out how to fix this "glitches". So, use your own judgement and keep your eyes on the bill as often as you can via TMO web account. It usually is updated close enough to within 1-2 days for the call made via UMA overseas.
From my experience, if I am going to get charges for international call, it takes about 3-7 days until I see the record of that international call when logging into my TMO account online. This can get tricky. Again, I am only saying from what I see from my own experience.
Just as the above poster, I also recommend that when making international UMA call, from Mobile Network Options make sure that the setting is set to be "WiFi only" option. I think that you will be safer that way. With this setting, keep in mind that you will likely get more dropped call as there is no UMA transition to the network in case your device looses wifi connection.
Good luck
Edited: As I mentioned in another thread but for the same issue, those calls were made after the 14th. When I first talked to the reps last Friday, the 14th were informed for the change to be applied.