Aren't those free wi-fi calls only for calls placed back to the U.S.? I've used that before in Europe since I changed plans but only for calls to the U.S. and it worked fine with no extra charges.

I did have 3 calls to check voice mail on my first international trip and was charged 20 cents per call, each less than a minute, and they went to the Germany number by default (dialed 1-2-3 on the phone when in Germany). I think the workaround there may be to call the 10 digit voice mail phone number in the U.S. while on wi-fi (area code 805). I didn't have any messages on my Hong Kong trip last week to check if that worked.

You can check your voice mail on the web as an option. It's listed under "tools" on your TMobile account page. I just tested that out with a new message and it played back fine and I was able to delete it without any issue. No longer shows on the phone.