I would like to know why the callers aren't just sending an email in the first place. I never leave voicemails and almost never receive one because we do business by email. I rarely even receive a phone call that wasn't pre-arranged by email.

If the company is providing only a phone number and not an email address or web-based contact portal for customers or business contacts, I can understand why the callers are frustrated. Forcing them to call is not quite like telling them to send a fax, but it's an imposition.