My phone has always been with BT. My previous ISP was O2 LLU, and I migrated to IDNet FTTC in one step on 18 Feb. 30-minute job, no problems.
So that's a bigger jump than yours would be, as you are already connected to BT Wholesale kit in the exchange whereas I was connected to O2 kit. Though you may or may not need to be moved to different BT kit for FTTC, depending on exactly what you are connected to.
Many O2 and Be LLU users have gone straight to BT Infinity in the same way.
The procedure is no different to a normal migration, except the engineer visit to do the install is still necessary. That could very well change to user or ISP install by the end of 2012.
If your line rental was with someone other than BT and you wanted Infinity, then I would have recommended moving that first, nearer the time. That's why I asked about it in my first reply.
My broadband basic info/help site - www.robertos.me.uk
My domains,website and mail hosting - Tsohost
. Internet connection -
IDNet Home Starter Fibre. Live BQM
"Where talent is a dwarf, self-esteem is a giant."
- Jean-Antoine Petit-Senn.