I have found a similar difference between phones and email in my business.
I am a prostitute, and to get clients I advertise in the local newspaper. Normal practice is to provide a phone number as an initial point of contact. Using my cellphone was getting rather expensive, as was advertising several days a week. I also work as a volunteer for several non-profit community organisations, and there I found many people preferred emails to the phone or postal services. So I decided to try an email address instead.
The difference really surprised me. With my phone number, guys would sometimes make bookings then not turn up. Others sounded very creepy. However, using email I have had only two cancellations, and in both cases I was paid in full for the time they booked with me.
Then again, prostitutes who read New Scientist and volunteer at non-profits? Johns who pay for services not rendered? Was this letter phoned in or emailed?