I remember how dead set the government was against strong encryption for cell phones.
They have the SIM card data, they have the firmware, they made sure the flakey baseband processor was never cleaned up...and most of all they made certain that perfect forward secrecy was not implemented.
Still, there is a way to get hard encryption for the audio data... it requires an external Bluetooth headset with built in perfect forward secrecy crypto. To achieve security you need an external device since the phone cannot be trusted. The metadata cannot be protected though.
How can you trust an external device unless you build it yourself?
They have access all text messages and possibly recording of conversations stored by the their willing partners, the carriers themselves.