How to check the uniqueness of a phone number?

Hi all.
Write an application in which there is two-factor authentication. There was a following problem with validation of phone numbers: numbers written using +7 and 8 are considered to be different. In the database I would like all the numbers in one format to be stored. Began to think of how to solve the problem until the solution is ready and it is the following: I remove from a string all except numbers, check the first digit (if 8 and figures 11, change 8 to 7) if 10 digits, add the front 7. My solution works only for the Russian offer, and I would like to work with everyone. May be someone faced such problem and knows how to solve it.
July 8th 19 at 11:52

Find more questions by tags C#