A comprehensive regex for phone number validation

I'm trying to put together a comprehensive regex to validate phone numbers. Ideally it would handle international formats, but it must handle US formats, including the following:

• 1-234-567-8901


• 1-234-567-8901 x1234


• 1-234-567-8901 ext1234



• 1 (234) 567-8901


• 1.234.567.8901


• 1/234/567/8901


• 12345678901

I'll answer with my current attempt, but I'm hoping somebody has something better and/or more elegant.