The expertise to do these things is the domain of well outfitted organizations, who have other simpler methods of making you talk. Indeed, electronic surveillance of is often used to protect agents from dangerous work.
Yes, but numerous people participating in the Osmocom projects have that expertise. Fortunately, they're interested in building an open-source baseband processor (among other cool things), and not in hacking into anyone's private communications.
Besides, base stations are available openly on the market now at pretty reasonable prices. It's why I never talk about anything truly private on a mobile phone.