VRI is mentioned, as in mentioned, not explained, in some Openreach PDF files. Like the one in this link:
If it's really bugging you why not ask Openreach?
Won't be any different, it is just broadband without a physical phone line as well.
Does VOIP burble like mobile phones do? I seldom use my iPhone (or the predecessor, my Blackberry) as a phone because the sound quality is so poor compared to my excellent BT landline.