Sending short messages is a GSM service. Our RCS dialers allow for sending SMS to offnet numbers. When you want to send an SMS to an RCS user you have to select paid SMS button instead of the default free instant messaging button. The composer and conversation screens look the same as for instant messaging with the difference that the attachments and geolocation features are not available.
In the chats list the threads related to the SMS are shown with the dollar icon indicating that it was the paid message.
The SMS service is usually chargeable. The rate for a given phone number is shown next to the send SMS button in the Contact details view. SMS rates are also shown in the Account/rates menu.