Thanks for the heads up on the voicemail. I just found the small print on the t-mobile website:

Unless you switch your device off or activate Unconditional Call Forwarding on your device, you will be billed for calls delivered to your voice mail box while you are roaming internationally.

I'll just turn the phone on when I need it. I'm on vacation, I don't want the distraction of that thing ringing anyways =)