I signed up to Google Voice with the help of a friend in the US.

I tried using the Android app for make a call but it doesn't work properly. It always fails with some unknown error and the recorded message tells me to try again later.

I'm mostly using it for the free US text messaging as most of my friends in the US appear to have a text messaging bundle. So the inability to make calls isn't actually a problem for me at the moment. I've noticed that if you get sent a MMS then Google just silent drop it without notifying you.