some interesting stuff there; particularly the use of the cheap RTL-SDR for GSM monitoring.
As far as I am aware it is perfectly legal in EU/CEPT countries to monitor your own wireless communications [or others you have permission for such as at your employer] using these devices.
A heads up that some of the projects that involve building mini GSM base stations can get you in bother if done in the wrong place (as they could disrupt the main networks including 112/999 calls) but it is actually possible to get a small scale experimental license for these units from most European Communications Ministries (i.e Ofcom, Agentschap Telecom, BNetzA etc). This is fairly new; something to do with CEPT/ERO in Denmark encouraging people to learn about wireless communications.
I had wondered how a hackerspace in NL had managed to set up its own GSM network (that links to the internal phone system) without getting bother from Agentschap..
You do have to fill in some paperwork, declare that you are not using it for intercepting/forwarding any traffic from the national networks and tell them exactly where you are operating the device (there is usually a small admin fee but often less than €100 for up to 5 years). It is not a requirement to have an amateur radio license but the profs at the Communications Ministry are more likely to be supportive if you do, or at least can prove you know one end of an antenna from the other and how to avoid causing harmful interference. The equipment must be either a certain distance away from any public GSM base station (or safely within a Faraday cage so no stray signals escape) and limited in transmitter power output; although anything affordable is only going to be a few milliwatts power output (TBH you don’t want to be standing too near to anything stronger as the radiation isn’t good for you…)
