A simple solution would be to offer an alternative for verification.
To be more helpful, chances are unless your phone line is in a business, you don't have an extension.
I am a designer for both print and web, and I remember when designing websites and mockups.
Your users should not wonder which phone number format is valid or get a validation error for the wrong phone number format.
You can only include the plus sign at the beginning of the phone number, as shown in the formats above.
I was told to just keep trying different numbers until it worked.
Feel free to drop us some ideas anytime at Badoo.
Lack of leadership, cheap and disgusting service really! And a word about guidelines: guidelines are not out of the box solutions.