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The International Telecommunication Union (ITU) has established a comprehensive numbering plan, designated E. 164, for uniform interoperability of the networks of its member state or regional administrations. It is an open numbering plan, however, imposing a maximum length of 15 digits to telephone numbers.
Use VARCHAR to Store Phone Numbers in MySQL The final suggested method for handling phone numbers in MySQL is by using the VARCHAR data type. VARCHAR offers the flexibility of dynamic memory allocation when the phone number length will vary across database users.
Always specify a length to any text-based datatype such as NVARCHAR or VARCHAR .
Assuming you don't store things like the '+', '()', '-', spaces and what-have-yous (and why would you, they are presentational concerns which would vary based on local customs and the network distributions anyways), the ITU-T recommendation E.164 for the international telephone network (which most national networks are connected via) specifies that the entire number (including country code, but not including prefixes such as the international calling prefix necessary for dialling out, which varies from country to country, nor including suffixes, such as PBX extension numbers) be at most 15 characters.
Call prefixes depend on the caller, not the callee, and thus shouldn't (in many circumstances) be stored with a phone number. If the database stores data for a personal address book (in which case storing the international call prefix makes sense), the longest international prefixes you'd have to deal with (according to Wikipedia) are currently 5 digits, in Finland.
As for suffixes, some PBXs support up to 11 digit extensions (again, according to Wikipedia). Since PBX extension numbers are part of a different dialing plan (PBXs are separate from phone companies' exchanges), extension numbers need to be distinguishable from phone numbers, either with a separator character or by storing them in a different column.
Well considering there's no overhead difference between a varchar(30) and a varchar(100) if you're only storing 20 characters in each, err on the side of caution and just make it 50.
In the GSM specification 3GPP TS 11.11, there are 10 bytes set aside in the MSISDN EF (6F40) for 'dialing number'. Since this is the GSM representation of a phone number, and it's usage is nibble swapped, (and there is always the possibility of parentheses) 22 characters of data should be plenty.
In my experience, there is only one instance of open/close parentheses, that is my reasoning for the above.
It's a bit worse, I use a calling card for international calls, so its local number in the US + account# (6 digits) + pin (4 digits) + "pause" + what you described above.
I suspect there might be other cases
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