This is not a development issue as it is a business one, I think just advanced people can get this one answered.
When operators are going to bill their customers via SMS messages, there is two types of how this could be implemented:
1. Mobile Terminated billing: The user get paid once the SMS recieved.
2. Mobile Oreginated billing: The user get paid when he/she sends a message to a billable short code (Premium Rate Number).

What I want is a trusted resource that explains those types in details, I tried lot of major web sites but all of them are talking about hardware/software support. What I want is the idea from a business point of view. Any reply will be highly appreciated.

Nabieh Salim.