Sometimes the lack of replies might also be down to the number of emails being sent to them. From having chatted with a few people it is not uncommon for some girls to get dozens of emails every day, with several questions in each, and it is also not unusual for people to discover that having answered emails and specific questions that more emails and questions get sent and some punters seem to get off on sending out lots of emails to lots of girls every day asking loads of questions without having the money or time to meet everyone they are emailing.
One of the girls I've known for a while, just gives out her number, days and times she is working, asks folks to check her availability diary and FAQs and likes list and says for any other questions phone or text her. She answered 18 emails in 2 hours from one punter who was going to make a booking and was only 5 minutes away and 2 months later they still haven't shown up.
I'd agree its better to phone, and would say sometimes there are valid reasons for girls not using email much.