makes sense
Premium texts are SMS sent to / received from special short code numbers. These are promotional messages that usually provide information or entertainment and are charged at very high rates by the networks. For instance, sending a text, like a vote for a Big Brother contestant; receiving a text like an order for a ring tone; receiving texts on a regular basis (called subscription services), like a daily horoscope falls under premium texts.
Other examples of premium text services include mobile game downloads, sports results, adult entertainment and information services (weather, traffic, etc). Both incoming and outgoing premium texts are chargeable and in certain cases, an incoming premium text may be more expensive than an outgoing one.
This information is also stated on the Matrix Customer Agreement Form (CAF), signed at the time of getting a Matrix product/service.