According to a VoIP list moderator about Google Voice outside the USA ...
You don't get full usefulness from GV unless you are in the USA.
You will need to register from a USA IP address.
You will need a US phone number to send calls to, in order to validate the account.
GV does not easily connect to SIP. (Addition by Suzanne Bowen: but that is why Google bought Gizmo5.)
Outside the USA you can use GV for sending and receiving SMS.
Outside the USA you can use GV as a place to get voicemail.
Outside the USA you can make free calls to the USA only if you have a USA DID or a Gizmo5 account. There may be other hacks, but I don't recommend depending on any of these. Gizmo5 is less than 100% reliable.
(Show me a voIP application or cell phone service that is. None, none at all. The fact that the person says Gizmo5 is less than 100% reliable... congratulations, Gizmo5!!!!)
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