I also have trouble believing is that 3G/4G networks would not be affected. All of these protocols are based on symmetric cryptography, i.e. a shared secret between Operators and their SIM cards. Once you get the shared secret you have the keys to the kingdom.

Their protection is that many MNOs are using proprietary authentication algorithms, making it harder to scale global surveillance. But that applies equally to 2G/3G/4G.