Correct. Phone call and texting via non secure methods would definitely be stupid.

Assuming what Q said was correct about Q being a group of people. Do you think they are always together? I imagine military intelligence has very secure ways to communicate that we are not privy to. Hell, even just using public encryption allows people to securely communicate. Unless there's a quantum computer that can hack encryption. Otherwise it is very difficult and would take decades to hack using the best super computers we know of.