(Of course better and newer models would also have voice capabilities, but that comes later.)

Start off with a walky-talky like pair of low-cost PDAs except you dont talk but can only "SMS" each other. (Sold as toy for kids).

Continue with Wifi or bluetooth to PC.

Use PC as relay station - connected to the regular internet in broadband. People can even get payed for giving the relay service. (works only for people in the local vicinity).

Within a short while you'll have people able to pass and recieve information on local networks around the world, without the need to pay the cellular companies.