PS: using 2way radios for data transmission might be a subject to your local telecom regulation.
I was about to post something different, then I saw your last line. This needs to be stressed; depending on what you plan to use as a 2-way transceiver system, you will need and want to find out whether you can even transmit data over it in the first place (with or without a license).
For instance, here in the United States, while you don't need a license to use a "family radio" or to use a CB (citizens-band) radio, technically, you aren't allowed to transmit data over either. I'm pretty sure that even if you have a ham license, you can't do it - at least on those bands.
Now - you could probably get away with it, at least in the short term. Maybe if you channel hopped as well, you could get away with it longer. But sooner or later, you might have the FCC knocking at your door (again, here in the US). Actually, I'm not even sure that would be the case, even in the case of CB radio (which seems to be mostly "dead" as far as usage in some areas).
I'm not sure whether the same would apply to cheap FM toy walkie-talkie systems; likely for these nobody would give a damn except for any other kids in the area (though again, their interference is -your- interference as well - so take that into account).
Now, if you have a ham license - the possibilities will open up quite a bit (though the amount of money needed to implement the systems may also increase); personally, I would just stick with whatever I could get off the shelf, and try to keep things within legal power limits, to limit my exposure to all sorts of fun limiting authorities.
There's plenty you could do with everything from xbee, 802.11x network stuff (technically xbee falls in this realm), 2.4 GHz R/C systems, and those other small transceivers that operate in the 900 MHz and other bands (not to mention some of the bluetooth stuff). These, coupled with appropriate antennas, can easily cover a quite large area for control, telemetry and other operations, and won't get you in trouble with the law - if that is a concern in your locale.
If you need longer distances, there's always cellular-based data systems, and if you need really long distances that can't be spanned by the cell phone network (ie - things out in the hinterlands) - satellite data is also possible (though not cheap).