Just put +1 in front of the number.
If you store all numbers using + followed by the country code this means you can always text/dial from any where in the world.
So store all your Uk numbers as +44 and then the number leaving out the first '0'.
You can't tell the difference between land line numbers and mobiles in America unlike UK which has 07 numbers. Anyway as someone said its 001 then the number i.e. 805 498 4563 and that should work. It costs about double though so remember that !!