A small operation that doesn't take calls has probably learned they cannot conduct their business because of endless, unanswerable questions about which plug or cable will work best with an amp. The owner would rather field questions via email, where he can control the length of the exchange in order to have time to fulfill orders. Chris at VH Audio gets my orders to me in < 72 hours, gets back to my questions via mail and solves problems with orders just as well as if by phone. You should not have a problem with this business model. A real problem would be the seller or buyer on this site who doesn't like to talk via telephone regarding the risky purchase of a used product, sight unseen. There's a transaction that will not occur.
Would you buy from a firm that has a policy about not accepting phone calls
Personally I would not. Call me old school but to me communications are the most important thing in handling business situations. Sure e-mail, faxing and texting are all great but nothing makes up for personal service you receive from getting a phone call.