Umm, I believe that more specifics about your current setup would help elicit responses from the knowledegable types here. Specifically, what are you running now and what type of kit are you considering?
The 10/100 transfer rate refers to Ethernet or Fast Ethernet; that is, at how many Mbps can you communicate with other machines. Which you get depends on cabling, other equipment, etc. Being on the telephone and being online are not necessarily mutually exclusive but may be depending on how you connect with the outside world (like the Net).
Are you looking at one of those HomePNA or HomeRF kits? Or....