Sender telephone number: sender phone number (fictitious) shown in the message received from the user. Except for Twilio, the other services allow you to insert an unreal number.
Alphanumeric Sender ID: enter the text that should appear as the sender (this option might not work correctly in some countries, check your country with the SMS service provider you have selected).
Admin phone: enter here the phone numbers of the admins who will be notified via SMS. Include country calling codes. You can also specify more than one phone number. Type the number and press Enter to add a new one.