I'm honestly a bit surprised that they haven't really been pushing "using Tor for piracy" to create additional cover traffic.
Email has many problems but may be better than most, but you need to use something like gmail which everyone is using, and even that may be noticeable.
Once they suspect you, you're pretty much done for unless you find out that you're on the list and you stop communicating outbound. It's much harder to track one-way broadcast communications (many still think that there are/were communications to spies hidden in BBC shortwave broadcasts, and numbers stations are still a thing).
so —in principle— the minutes field could be used to provide a very low bandwidth covert channel on top of innocuous commentary. Wouldn't it be pretty difficult to pick up even an outbound one-if-by-land two-if-by-sea style communication from the general noise floor?
Email has many problems but may be better than most, but you need to use something like gmail which everyone is using, and even that may be noticeable.
Once they suspect you, you're pretty much done for unless you find out that you're on the list and you stop communicating outbound. It's much harder to track one-way broadcast communications (many still think that there are/were communications to spies hidden in BBC shortwave broadcasts, and numbers stations are still a thing).