International Callback Dialing Rules?

Ok I have not messed with dialing rules in a long time just because for the most part they work fine out of the box. There have been a few providers that needed 01 instead of 011 so no big deal. Here is my question I post in the wee hours of the morning.

Suppose I have someone called back internationally based on caller id? The international number of course is not going to be preceded by a 01 or 011 so how is the system to know to treat it as an international number? Perhaps by counting the number of digits dialed?

Ie his caller id was 442072339670
Thank you