You haven't dialed internationally before, I take it?
From the US, you need to prefix any full number with the country code, and if applicable, city code. All US int'l dialing starts with 011. For example, if I wanted to ring a friend in Melbourne, Australia, I'd dial 011 61 3 9xxx xxxx, where:
011 = international
61 = Country code (Australia)
3 = city code
9xxx-xxxx = person's phone number (in 1995, all local numbers there were given the 9 prefix before the actual number).
So in your case, the number would be 011 50 xx xx xx xx.
my GV number is a standard phone number actually picked from my area! not sure why his would be different! why not have him text call you and just add it to his contact!