the White House has, for the past decade, provided more than $6 million to the program, which allows the targeting of the records of any calls that use AT&T’s infrastructure
the program takes advantage of numerous “loopholes” in federal privacy law
the DAS program has been used to produce location information on criminal suspects and their known associates, a practice deemed unconstitutional without a warrant
(This website is a bit annoying.)
Just now (~ 1 hr ago), EFF also recommended Signal.
https://ssd.eff.org/module/how-to-use-signal How to: Use Signal | Surveillance Self-Defense Last Reviewed: October 31, 2023
(I also agree with you about simplex, still too early and iffy.)