I had been with Zen Broadband for over 12 months when,in December, I decided to join their Home Phone Service.
Before doing this I checked with Zen that I could move either Phone or Broadband away from them independently if i needed to. They said this would be fine.
Earlier this month I migrated my broadband to another provider, no problems with Zen they had been excellent, it was just that I was at last able to go to an LLU provider at my exchange.
So, I still have my Home Talk Plus with Zen and get BB from my new unbundled supplier.
BTW I find the Zen phone service excellent and it is actually working out cheaper than BT which was not the main purpose of the switch, just a bonus.
iSight G5 Mac. Zen 8000 active