If you work in an office, your work days include the standard routine of commuting to work and taking your place at a cubicle in a corporate facility amid your fellow employees.
Most likely, your employer has provided you with a desk and a laptop, and on your desk is a telephone connected to the corporate multi-line telephone system (MLTS) known as an MLTS/PBX. Alice in accounting or David in sales is easily reached by directly dialing that person's extension number. Reaching someone outside of your company is just as easy. First, an access code is dialed, then the 10- or 11-digit telephone number of the desired remote party. The rest is telephone network magic that is likely out of sight and out of mind.