I suggest storing the numbers in a varchar without formatting. Then you can just reformat the numbers on the client side appropriately. Some cultures prefer to have phone numbers written differently; in France, they write phone numbers like 01-22-33-44-55.
You might also consider storing another field for the country that the phone number is for, because this can be difficult to figure out based on the number you are looking at. The UK uses 11 digit long numbers, some African countries use 7 digit long numbers.
That said, I used to work for a UK phone company, and we stored phone numbers in our database based on if they were UK or international. So, a UK phone number would be 02081234123 and an international one would be 001800300300.
