Walt,
You can set it up for using a specific line, pool, or routing code (if you are using the routing table). You will have to play around with pauses and such to get the right timing for sending the pager info. A butt set is invaluable in this process. I always select a line first (so I know which line the mail is going to use to dial out), connect a butt set to that line, leave a message in said mailbox, then listen (via butt set)to the transaction with the pager in front of me to verify it works several times in a row (this makes sure you have the right digit string and the proper amount of pauses). Then, I go and change the outdial to pool or route or whatever and test once more.