NANP format ( 1+10 digit on US calls and 011 + CC+ on international calls) should be used. For more information on North American dial plan formatting, visit www.nanpa.com & for more information regarding E164 formatting, view the following PDF online at www.itu.int/dms_pub/itu-t/opb/sp/T-SP-E.164D-2009-PDF-E.pdf.