It's reasonably clear my end and I am on Vodafone so coverage as bad as all the others.
Specifically people say the background noise and feedback with echo is so bad it's not possible to continue. I've been using car phones for years and this is the first time such continued issues are present. My iPhone in my wife's Golf or other hire cars is fine.
It may be my car specIfically and I wondered if it may be a compatibility issue between the car and phone - maybe the mute effect??