Firstly is the Link to Avatar itself: telnet://play.avatar.co.uk
Technical Bit for users who know how to set up their client software:
Avatar uses 'No Echo' when communicating with clients, therefore you must setup 'Local Echo'. It uses ANSI colour sequences to display text.
For the rest of you - who didn't understand the above sentence:
If you are not using any special telnet clients then this should open a connection window like this: