Technically speaking, Voice Over IP is the ability to stream audio over a network, but in the industry, "VoIP" means making telephone calls over the network using the IP protocol.
TOIP is a term (that I had never heard of before reading this question) that seems to be a little more specific in that it connotes telephone calls (which includes the voice and signaling required).
In practice, use "VoIP" and not "ToIP". Everyone will know what you are talking about.
just my two cents.
