The carrier is required because Kicksite uses email to SMS. This feature is offered by most carriers in the USA. In order to utilize this feature, the carrier needs to be added to the phone number receiving the SMS. We send the messages out as an email to the recipients carrier, and the carrier then converts the email to an SMS message and sends it to the phone. It is imperative that the correct carrier is selected, otherwise the intended phone number will not get the message! If you don't see the carrier you need, please contact us. This is typically a free service offered by carriers, at least in the USA. It may not be so in other parts of the world.