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.

Gary


>>>I have an application that has to run in 14 languages and 17 countries. I check for counrty, use this method for U.S. and allow 'free form' in non-U.S. because of all the weird(to me!) phone formats around the world.
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>>I like this idea for U.S. phone numbers too. Is there any reason to format US phone numbers, especially when some have extensions and some do not?
>
>Yes, there's an insurmountable one :) Users do not like it from a readability aspect. Extensions go into a separate field, as they vary in length.