Still remaining (well ahead of the e-mail) the first communication tool between a company and its prospects, its customers and its staff, the telephone, and generally speaking the communication system, cannot be considered a work tool of secondary importance. The telephone switchboard is the brain of your communication system.
Also called PABX, the communication server sends and receives your calls, directs callers to the right person (direct line, call transfer), and makes sure your contacts are getting high quality attention. Similar to computer science, telephone technology is evolving rapidly, and provides services today, without which it becomes hard to win new customers and satisfy the existing ones.