The customer's mobile phone can be useful to you if you want to call him or send him a mailing list. And if in the first case a person can understand how to dial a client, then for mass mailing to clients, the numbers must also be of a single format, otherwise problems may arise in the mailings. It is recommended to use the international template of phone numbers in the pharmacy management program, where after the "+" is the country code and the rest of the digits. The number must be written without spaces
For example, +79991111111