The EFF Secure Messaging Scorecard lists a number of apps that meet all of its security criteria. So assuming that end-to-end encryption is accessible for the majority of people in countries in which encryption is legal, how do intelligence agencies listen in? It seems like in the case of a high-value target (Alice), the strategy would be to hack into Alice's endpoint.
I'm wondering about the security of mobile phones versus laptops. Laptop users have a bunch of choices to increase their security (use Linux instead of Windows, use TOR, use TAILS, etc.). But after reading this article I'm thinking about how cellular device users are stuck with a device with a baseband chip running a propriety O.S. that is in constant communication with a cellular company that is forced to cooperate with intelligence agencies. In other words, can't the NSA just ask Verizon to send Alice's iPhone malicious data via cellular that will cause her baseband chip to read something from memory (like her private key) and send that back?
In light of this concern, is usage of a device NOT connected to a cellular network preferable for keeping your communications private?