[ChuckMcM]

Like anything, it is technically possible to do this. As a defensive mechanism, I think it would make sense to perhaps hang out at city call and collects a bunch of IMSI's worth spoofing, and then rebroadcast those while you were being subject to surveillance, the goal being to force the adversary to follow down a bunch of leads which are bogus.

That said, this is completely illegal (unlike the actual surveillance which has been made legal by a series of unfortunate events). So I would not advise anyone to do this. Not to mention that unless you design your own cellular baseband radio circuit (so that you have access to all the docs) building something like this with "off the shelf" parts is quite expensive.

[archimedespi]

SDRs are no longer that expensive - even an Ettus or BladeRF device is within the range of the average middle-class engineer - and can be programmed completely in software to act as a cellular baseband device.