I've been with Be* for about 10 months now on their £17.50 package and I raised a ticket with them the other day saying that I wanted to switch to the £10 O2 Premium package since I have an O2 mobile.
Be* rang me back later the same day and said that if I wanted to stay with them, they could offer to keep me on my current package and reduce the monthly cost to £12.50 indefinitely. I decided to go with O2 anyway because it was cheaper (especially with the 3 months free that they're offering until 31st January) and I don't need the Be* gaming mode.
For anyone who does want to stick with Be* though, it's a pretty good deal. I thought that maybe someone on here would appreciate a discount.
A word of advice for anyone taking the O2 deal - You'll need a second email address and a different username when you sign up on the O2 website. The system will recognise you as an existing member because of your Be* account but they can't just switch that account over to O2's side of the system.