Bear with me since some of my history is sketchy...
I seem to remember the difference between the I and SI being the processor used (although I could be wrong). If my memory is correct, it basically is an age issue.
As for VoIP, it was introduced to the Definity in release 9.5. I seem to remember reading that you can install a C-LAN board into a R8 switch, but it won't function correctly.
Since I've never done it personally, I'm not sure how, but I know you can tie the Definity into other switches via T1 or Tie Lines.
Me? I'm still stuck on V6
