Forgive me for being so stupid. I want to sign up (register) in www.youtube.com
and they ask me for a mobile phone number to send me a text message. I begin the phone number with the prefix 15, which in my country is used for all cellular phones (which I think is the same as a mobile phone). However, they reply with the following message:
This phone number format is not recognized. Please check the country and number.
Any hint would be greatly appreciated. Thanks.