You can now install a GSM network using apt-get

I carved out an exception to that rule, to say something surreal. Have a nice fish.

If you simply don't understand what is implied by this headline it really makes no sense, despite every word making sense.

There are strict guidelines, but generally it is possible to obtain an experimental license for specific events/situations.

As "extrapickles" pointed out in another comment thread, the spectrum requirement for this is an even bigger hurdle than getting all of the expensive equipment together to pull it off. The tech requires an amount of frequency separation that spreads outside the bounds of the ISM spectrums, so you'd need licensing or would need to be running in a third-world country with no regulations (which is actually a viable use for the tech).

For the unaware, ISM = Industrial, Scientific and Medical. These are the shared unlicensed frequencies that the general public may use. Wifi falls inside of this range.

Sorrrrrrta. GSM the spec requires that 45 mhz of tx/rx spacing by convention, but GSM the technology as we colloquially know it, e.g. if you're code-shifting 2G (i.e. via CDMA) you could get away easily in the 900-928 range @ full duplex. No technical limitation at all there. This was briefly discussed in an older thread by myself and a few other chaps here[1] but I guess tons of other people have had the idea before too haha.

The US spec GSM phones operate at (a nominal) 850 mhz, but like you said there are plenty of eurospec (and asian spec.. and US issued quad-band..) which can operate with off-the-shelf with all the (again, nominal) 900 mhz[2] band tech that's being phased out. It will pick up, negotiate the handshake and route just fine. The issue is really just like any other cellular network: getting tens of thousands of antennas up, and having people buy new phones that are quad-band and/or carrying around an eBay phone for what amounts to a novelty.

I'm not on the cutting edge of milliwave or RF anything (all voodoo to me) but as I see Agilent come out with more and more sensitive test gear, I can only presume that the wireless industry is getting way better at tuning YIG's, VXCO's, eliminating side-band tone bleed, and what not. Much like the analog (i.e. 1g, remember those Motorola flip-phones? I do1!) -> 2g shift increased capacity by 3x, I'd have to imagine new encoding techniques and what not are being developed by the PhD's and postdocs. Who else is going to buy a $300k network analyzer otherwise, haha

[1] https://news.ycombinator.com/item?id=11414069

[2] If you talk to old-time HAMs they'll joke about how the FCC really regrets throwing away a few hundred billion dollars worth of band in that spectra alone. You can pack a lot of content into each Hz down down there.

Why would the handsets registering be out of the the ISM band? What if you bought a quad band phone, wouldn't that work?

Putting up a single, limited range BTS is not the same as full scale, functional GSM network. It's similar as creating your home network with OpenWRT flashed router and calling it Internet.

The answer is to work with legal spectrum owners (aka cellular carriers), which is what we (https://fairwaves.co) and other in the space are doing.

Someone mentioned that building a full networks (or even a full base station) is much harder than just apt'ing some software and snapping some cheap SDR. So we spent couple years developing an SDR which is more expensive than your typical hobbyist one (http://umtrx.org) - btw even hardware of the simple version of our SDR is open-source - and then couple years building a base station which complies with all regulations and has open-source in its heart (based on Osmocom obviously). And now we've added a bit of (unfortunately proprietary) glue and we can run fully fledged cellular networks for carriers - mostly in developing countries, as was mentioned before, because demand for simple voice communications is through the roof there. At the same time you can buy one of our stations for your lab and play with it as much as you want (get your test license first though).

So yes, you can't stop progress and technology gets cheaper and more accessible. Which is very exciting.