The MG5050 (Magellan) has wireless (for sensors etc) built in. You can have a mix of both wired and wireless PIRs, door sensors etc along with remotes for arming/disarming and activating outputs (open your garage door and/or gate for example).
For interfacing with other systems you would want to get the EVO with a PRT3 Integration Module instead of a Magellan (what I've got) or Spectra (non-wireless version of the Magellan basically). The EVO costs a lot lot more. But it is also a lot more capable. It supports many many more zones, access control (electronic door access/control), timed/scheduled output activation (I think) and the all important PRT3 module. The module supports both a basic ASCII based protocol and C-BUS. I'm pretty sure you could get zone status reports and arm and disarm the alarm via the module. There is a document floating around on the Internet that documents the protocol, or you can get it from Paradox if you have the login/know somebody who does.
Having said that, with the Magellan and Spectra you can get them to activate outputs to indicate the armed state or if the alarm is triggered. You can also set a "Zone" to be a "key switch" to arm or disarm the alarm.
I was thinking of upgrading to a EVO to get the PRT3, but decided it would be easier and provide more features to just implement the alarm as well instead of trying to interface with one. Of course you only get your "Alarm Installed" insurance discount if a proper one is installed by a professional certified alarm installer.
For really capable and interfacable, get a Concepts or Cardax/Gallagher :-).