Traffic analysis is a GREATER danger to innocent bystanders than recording calls, because it is all hearsay and unproven.
if they tap my phone calling for a takeaway curry then it's obvious I'm innocent. If they just log that I call that number and later somebody they are 'watching' calls that same restaurant (because their relative works there) then I am secretly linked to that person in some database - this doesn't get examine in court - but I now have 'links to terrorists'