I hate to break it to you, but essentially all Android and Apple devices on US carriers can (potentially as a capability, but it's extremely unlikely in the real world) be remotely screenshotted, location tracked, and microphone and cameras activated by US intelligence agencies because they can get whatever they want inserted onto endpoints (phones and other SIM devices) by the carriers. This probably happens in most countries. State actors therefore don't really need RCE or local priv esc 0days to break into any phone or backend, social engineer an engineering shop, or plant a spy software developer to gain in-app access. WhatsApp maybe good enough, but it leans heavily towards MAANG feudalism while Signal doesn't currently. Signal won't help this massive endpoint vulnerably either, but it's backed and design is more trustworthy. Only an audited FOSS hw/sw stack that doesn't agree to carrier and local regulations requiring unknown, untrusted code loaded on a user's device would. And, honestly, I'd like a phone that can switch to e2e voip automatically should the other party have Signal or similar installed rather than making a conventional call. IDK if Silent Circle's Blackphone 2 did this or not, but the Silent Phone app that replaced it defeats the whole purpose of a Blackberry-like device.