As someone that has written code to pick up the encryption keys out of the Diameter protocol, and used those to decrypt the control plane NAS signaling on the S

As someone that has written code to pick up the encryption keys out of the Diameter protocol, and used those to decrypt the control plane NAS signaling on the S1 interface, correlated this info with the user plane data between a S-GW and P-GW - no - LTE is not end to end encrypted. There's encryption between your mobile and a few nodes within the core network of your carrier - inside that network, you can easily break that encryption if you get hold of the keys - and those keys are communicated in plain-text between a couple of the network nodes (on the S6a interface). While those interfaces are supposed to be using IPSec, I've yet to see anyone doing that all the way. The radio interface, between your device and the cell tower is decently protected though. Unless you're in a country that demands the use of the EEA0 and EIA0 encryption algorithms (a.k.a. no encryption at all).