>User readability is a factor. I use a phone class that breaks out country code, area code, phone number and extension. Four textboxes in a container. I input mask and hide the country code textbox in the U.S. This seems to be a workable compromise for now. I may collect the country specific input masks at some later time. I may make the country code visible as a user preference later too.

Sounds like a good solution, and I certainly don't envy you having to cover all the various country formats, I've seen some of the different formats used around the world...