private void Init(string phoneNumber, TelcomProvider provider, BodyFormat bodyFormat = BodyFormat.Sms)
 {
     if (phoneNumber.Length != 10)
     {
         throw new Exception("phoneNumber must be length 10");
     }
     PhoneNumber = phoneNumber;
     Provider    = provider;
     BodyFormat  = bodyFormat;
 }
 public PhoneProvider(string phoneNumber, TelcomProvider provider, BodyFormat bodyFormat = BodyFormat.Sms)
 {
     Init(phoneNumber, provider, bodyFormat);
 }