I don't think it's a question of open hardware: To send a phone call to your phone, the mobile network must know the BTS/eNodeB/GnodeB associated with your phone.

While this is a large surface in rural areas and older technologies, it's not the same in urban/newer technologies. It could easily be associated with a given building.

To protect our location, it would need something akin to a mobile proxy that would relay the communication but to my knowledge, there are no such things for mobile communications. And this is not really secure, it's just outsourcing security to another entity which may be be compromised.

(I am quite rusty, but I was a telecom engineer)