Yeah there are lots of different interfaces for each PMS. For example take Opera by Micros Fidelio. They would one interface for phone billing, one interface for mini bar billing, one interface for GDS, for POS, for in room entertainment, for phone maintenance (enabling disabling n room sphones etc), for in wifi billing etc etc etc. So Basically one PMS will have multiple interfaces each for specific purposes. I have no idea what solution you are thinking about but lets say you were thinking of providing wifi to a hotel chain(for the purposes of our example). Now the hotel chain use Opera as their PMS. So you get the spec for that specific wifi billing interface. Then you pay them for the access to the interface and a test system and then you would write your code to enable your system to communicate to that interface. It all goes thru their testing in their mothership and its either approved or denied etc etc etc. Its a slow. process.
Not sure if this is any help to you. I understand why you might be apprehensive about giving more specific details in your scenario but without that Its hard for me to be more specific and hopefully more helpful in my answers.
