Can you give us more background as to where you are getting this information? Is it on your servers?
the information could be drawn from several different things including model numbers of different servers. What I have found is that a T-server is a Transactional Server and an I-Server is an intermediary server when working within a communications server environment.
give us more information as to what type of environment you are working with and where you are getting these names and we will be able to help you out with more detail.
For T-Server see http://wiki.answers.com/Q/WHAT_IS_a_genesys_t-server