So suck it up and return those calls - immediately. Procrastinate and the messages will pile up into an hour's worth of telephone time. Find out what's wrong and deal with it.
Use e-mail more. Get into the habit of using e-mail for routine communications with employees, customers, suppliers and everyone else you come in contact with day by day. You can dispense with a dozen e-mails in the time it takes to complete a single phone call.