What is the max and min digits for an international telephone number? (country code + area code + phone number)
, where the format of telephone numbers is standardized by ITU-T in the recommendation E.164, which specifies that the entire number should be 15 digits or shorter,
Source: http://en.wikipedia.org/wiki/Telephone_number
Also, check this other question on SO: What's the longest possible worldwide phone number I should consider in SQL varchar(length) for phone