GSM, CDMA2000, and other cellphone technologies use published standards. Now instead of transmitting at 100 watts of power from a cellphone tower, like the professional cell service provider companies, what if I instead had a small dongle that operated at FCC Part 15 low power levels for unlicensed devices (think in the range of 1 to 10 milliwatts)? Such a signal could theoretically provide cellphone service up to maybe 20 to 50 feet from the transmitter. A small area of cellphone service coverage like that is known as a "picocell" or "femtocell". That would be really cool. If for example I had a USB dongle that could do that.
If I brought my cellphone within range of the dongle, it could lock onto the signal from the dongle, and my cellphone would then have service from that dongle. Of course, it wouldn't be able to reach any landlines, because (unlike with normal cellphone service companies) such a dongle wouldn't bridge the wireless phone system to the landline phone system. However, any phones that had locked onto the signal from the dongle could communicate with each other, like walkie talkies, but with the advantage of having a FULL DUPLEX conversation between the cellphones (unlike walkie talkies with PTT that only are half duplex). The provided software and drivers for the dongle would allow you to set the phone number of any phone that was on the femtocell. When a phone communicates with a base station it sends its wireless serial number to that base station. The software would let you then assign a phone number to that wireless serial number. That way, that phone would have a phone number on your femtocell, and that way other phones on the same femtocell could call your cellphone.
Unfortunately, I can't find any USB dongles that are designed for this. I searched "picocell" and "femtocell" in Google, and all I found were cellphone range extenders designed to extend the range of an already existing professionally-provided cellphone service (basically repeaters, so that if you already subscribe to a service like Sprint or Verizon you can get the signal if you happen to live in a spot not covered by their massive cellphone towers). But these are just range extenders or repeaters. They aren't true femtocell or picocell dongles. They don't create a new cellphone service, just extend the range of an already existing cellphone service.
If anybody here knows if there's a good USB dongle out there that generates a cellphone service femtocell or picocell, please let me know. I've always wanted to experiment with cellphone transmissions, without having to worry that Verizon might kick me off their service for experimenting with their signal (dialing special service numbers and other things you are not supposed to do, because they might think you are trying to hack them). If I could create my own separate service not connected to any professional cellphone service providers, I could do much more experimenting with my cellphone's hidden capabilities (that are usually in hidden debug menus and stuff in the phone). Also, as I mentioned before, it could make cellphones usable like fancy walkie talkies. And furthermore, it could also allow you to provide internet service to your cellphone, if the USB picocell/femtocell dongle also bridged internet access from your computer that the dongle was plugged into.