An advantage is also that almost any operating system supports Telnet. UNIX, and Windows 95 and NT as well, have such a Telnet program built in. What can also be used is a so called 'mud client' program. For windows, zmud is a popular one. For UNIX based systems, tinyfugue is popular.
Mud clients offer various extras to the mudder, and basically make life easier.
For more information see the mud faqs, posted frequently in rec.games.mud.anncounce.