This is the place to discuss generalized scanner questions and information for San Diego County. Whether it's radios, antennas, or other general scanner related topics, you can talk about it here.
I'm becoming very familiar with basic scanning (trunking, digital/analog, programming different systems and what-not) but I've never caught onto "paging systems". Is this something that the city implements? Where did you get hired?
IPN is a notification service that sends emails to pagers, or anything else that can accept (small) emails notifying subscribers of newsworthy events going on in their areas.
The 'official' news agencies use them as backups, to help them catch anything their own dispatchers missed, and they're useful for scanner listeners who want to be told if something major is going on they might want to get listening to.
Being a dispatcher for them isn't a paid position (well, not generally), it's just a volunteer thing scanner listeners can do, which earns them credits toward use of the service otherwise, and a few minor 'prizes'.
I should say, if you actually want constant 'hey, this is happening' info, the paging groups probably won't give it to you, as they specialize in the more newsworthy stuff, and also, even if, say, I hear a 2 alarm fire going down, unless I catch (and write down) the address, something you often never hear after the first dispatch on the air, I can't page it out. Pages have to have full info, by policy.
A real 'local scanner fan' group would be better off, perhaps, to arrainge an IRC chatroom for them all to hang in, or better, if they feel well enough off financially, perhaps to set up a GMRS repeater that covers their area, and get licenses and good radios so they can actually have a live net running with things like 'Did you catch that? Highrise, but nothing showing.', or 'Another fire in that damn Oceanside riverbed!'