Well from my homework so far I've come to the conclusion that signal is more secure and private than sms/standard voice calls. SMS is transmitted plain text, can be snooped on by hackers, saved by the telecom companies or intercepted and saved by governments. Although I think sometimes they just collect metadata, not the texts themselves, but I don't know. Same goes with voice calls. Signal is E2E encrypted, so all those worries are negated as long as the encryption isn't back doored. That's why I'd prefer to use signal. Please let me know if there's any errors in my analysis.