GSM hardware is probably the mostly regulated consumer RF hardware out there, it's also the most easily traceable.
Both the imei and the iccid of your sim card are unique and identifiable.<p>In some countries you won't even be able to buy a pre-paid sim card without an id at tmobile in Germany couple of years ago I was asked for my passport when buying one.<p>Even in places where it's possible there will still be a mile long trace, even if paid in cash.<p>Also since mobile phone tracking was a very hot law enforcement topic since the 90's even passive air borne scanners can pint point a handset to about 10m accuracy with ease, when combined with ground sensors and carrier telemetry they can pinpoint to which room of your house you are in.<p>So yep cool and nifty but if you are in a position in which privacy means life stay away from mobile RF as you are much better off hiding behind commercially available 1.8-5ghz radio traffic with a couple of relays. Also while mono directional antenna's give good signal and also make the signal less noticeable if some one even gets a look at one of the end points they can also easily pin point the other's location if they got highschool/entry collage level physics in their toolkit.
It is cheaper (+ better looking, weather proof and piece of cake to configure) to buy a couple of Mikrotik routers.<p>You can get them with multiple Wifi interfaces, LTE and everything else and configure it more easily.