[jyl]

The issues, I think, are the limited range of radio devices and the availability of frequency (spectrum). Spectrum is regulated, certain bands are reserved for police, fire, commercial radio, ham, FM radio, mobile phone, aviation, military, CB, FRS, GMTS, etc etc, and each has a legal power limit. A device would have to fit into a legally available spectrum. And then range is subject to the physics of that wavelength with the feasible antenna design and the legally mandated power. For more range you need a repeater infrastructure.

You can get approximately what you are describing with a FRS radio, these are the inexpensive walkie talkies you can buy at Best Buy. Range up to 2 miles with no obstructions, several blocks in built up areas (think Manhattan). For more power and range, get the GMTS walkie talkies which require a FCC license that is easily obtained. For even more range step up to ham radio handheld units, though more stringent licensing applies. All of these are open communications meaning others can hear what you say (no scrambling). We have some FRS radios, come in handy when hiking, flea markets, etc.