Wether you speak to them on your cel phone, email or any other method you have to have the self-discipline to NOT flirt or reach out. Every man is different about this, and if you are banning women from calling you on your cel phone (to me) it speaks to your lack of self control.
Then again, with his history I wouldn't blame him for taking this approach. He knows what works for him. When I was married and had a car I would often drop anyone that needed a ride off (co-workers, friends of friends etc) and if I didn't know the female I made her sit in the back. I looked like an Uber driver but so be it.