"Google Voice Plugin..." *is* The One Ring.
The issue there is that Google was faster setting up the callback than TOR is in realizing there wasn't and error and closing the call. So the call would come in but Maemo wouldn't let you pick it up because in theory you were in a call.
There is a bit of a complicated debugging step that I'm tempted to ask you to do (it involves the command line) but I think if you give Dialcentral (my other app) a try than we can get a feel if it is an issue with the front end or backend.