Here is how one person did it: Cingular rolls out BIS 2.0 & Unl Price drop!
Yes I did,
What I did was have CS delete my BIS account, then when I went to add it, it automatically took me to the BIS 2.0 setup process.
When i noticed the problems, I had CS delete my account again.
Then I loged on to BIS 1.8 (which I have setup for a different blackberry)
When I logged out from that specific account, I pressed the link on that page to log-in again, and this time it took me to the old BIS login (1.8) instead of the new one. Hit create a new account and voila!, back to 1.8
So yes, I was able to go back.
Part of this thread: Cingular rolls out BIS 2.0 & Unl Price drop!