I think that part of the problem is that US numbers are today often written 555/555-1212 instead of with parens. If you do decide to force the use to put the US Area Code in parens, please, please tell the user. I hate to see an input box on a web form for telephone number, enter 555/555-1212, and get some javascript error that I cannot decypher or perhaps some rejection from a CGI script that the number is incorrect. If you intend to force a format, please let the user know.</rant>