I respond to this question tentatively. I currently have the T-Mobile Simple Choice plan and also have Vivo for domestic Brazil calls. Since my monthly Vivo limits have been exceeded the last few months I have been trying to use T-Mobile. So far I have managed to use Skype while on T-Mobile data roaming. Is that the norm? I have no idea, but I think they do not intend for that to work. It has worked for me so far in Malaysia, Singapore, France, Russia, Brazil and South Africa. Even so, I do not actually expect it to continue to work.

I may be conditioned to expect problems...