I have only used Google Voice/ Chat in the US and there is a mention that the service is only available in the US. However when you read the warning it does not mention anything about IP tracking.
It says the following:
Don't see the Call phone feature? At this time it's only available for use in the United States. Please ensure that your Gmail interface language is set to English (US).
I dont know if it checks the IP (it does say only available in the US) or just your language settings but maybe worth a try
Original Source