We're not using APRS for messaging-yet-but that was the primary reason for starting this so many years ago! DonC could you hijack this thread or start another to fill us in on how y'all are doing that?
OP (and all) if you're a podcast listener-these are pretty informative:
http://hamradio360.com/?s=aprs
SC and all;
I moved here in February 2017. While I had been a member of this club for a year prior, I only started using it when I moved here. From what I can tell, it's a collective of a few igates here and a few in the surrounding cities. I'll get the full details. But suffice to say, they had these setup long before I moved back.
Now, to the how! Most of the HAMs here have APRS capable radios in their vehicles or at their homes. They are monitored regularly. As stated, some use it for tracking purposes via Skywarn and the rest of us use it for messaging. In my case, I cannot afford an APRS capable radio as of yet, so I used an old Baofeng UV-82, a BTECH APRS-K2 audio interface cable, and an older Android smartphone. I use APRSDroid because it has built-in messaging capabilities. I use this primarily in my truck. Once it's up and running, it'll populate the app with whois pinging the igates. If you can see them, you can send them a message.
One key thing to remember is: RF to RF or TCP/IP to TCP/IP when it comes to messaging. Example: anyone can open the APRSDroid app and even without a radio attached, you can track other TCP/IP people, but that's about it. On the flip side, people with radios attached can see and track either mode. However, you can only message other RF people. You can't cross message yet. (Kinda doubt we'll be able to).
I'll ask around when I get a chance and see if I can figure out our exact setup. But I'm fairly certain I'm close.
Finally, surprise, surprise, Carl is right, HAAT is important. Our igates are on top of a mountain, on top of a water tower, and on top of the radio stations tower, all more than 100' up.
Hope this helps. I will be out of pocket for some time for family matters, but I'll monitor and chime in as I can.