Packet radio is pretty far area coverage, like 20 miles or so. But within 20 miles, well you know where you are anyway so why spend the $400+ on ham equipment? I know HF bands go farther, but they are less reliable too.
My recomendation: I hear boost mobile's i415 will function as a 19000 baud modem over usb without using any credit on the phone, the phone is cheap, and you only need to credit the phone every 3 months or so $20. Get that.
It is a heck of alot easier making a auto connect to the internet script than trying to figure out how to interface and automate text messaging to a different phone. And to make all that obsolete, the phone has a GPS built in (nextel based) so you wouldn't need your own, and there is a third party app for transmitting with it. Check it:
It notes that web costs .20 cents a day, but maintaining live service means crediting about .22 cents a day to the phone anyway, so its like the service is free if you keep the phone alive.