IDEA: Who does not take calls from customers? Have them forwarded to the sales manager.

Ask your receptionist to inform the sales manager which people  in sales repeatedly does not take or return calls in a timely manner.  Instruct the receptionist to forward these unanswered calls to the sales manager or his boss. There are some people in life who are not made to deal with customers.  Find out where those people are in your organization and transfer them or terminate them.  Whatever is done, hire people for the position who enjoy speaking with customers.  Start getting this feedback immediately and resolve the issue.