Hi David,
We never 'hid' every, and I mean every, email or message we received was replied to. There are many successful companies who operate without telephone numbers.
When we introduced the phone number we even had a few people contact us to say that they felt it was unnecessary, partly because they felt they had received good service with communication by email. So I guess it's all down to personal preference. Email also has the advantage of being available at all hours, and keeping a record of conversations so things don't get missed.
In the early days of the company it was mainly a case of not having enough people/time to answer the calls. I've always felt that, worse than not having a number, is companies that have one that's never answered! We introduced the number when we felt we would be answer it enough of the time to make it worthwhile for us and customers.
Paul