So, for example, if one was 3 weeks into a full LLU 30 day trial offer and at that point gave notice to terminate then one would hope that the line could be returned to WLR before the end of the 30 days in order that one could migrate the BB to another provider.
They just require notice before 30 days, so you can give it day 29 - although actually migrating back will take much longer.
It's a strange one because Sky are offering a 30 day trial. They are letting the op leave as long as they give notice in that 30 day period. Whether Sky should pay associated costs to move to another ISP is debatable, afterall if they go to TalkTalk it would be a free transfer, if they go to BT - chances are it's a free transfer. If they go to someone smaller that's not mass market chances are it's not free. Sky didn't choose to pass on the charges to the end user, the receiving ISP did. Sky let the customer leave in 30 days as agreed - they didn't promise to use WLR.
Most people switching between a mass market ISP will find they are not using WLR. The big players are really BT, TalkTalk, Sky & C&W providers definitely have a market. If I move from BT for calls, line rental and broadband to TalkTalk, AOL, Sky or Post Office I lose WLR. It's almost a standard part of switching now if you require the best deals. There's only a narrow few providers who keep you with BT line rental, we're talking BT and Plusnet as the major players. I cannot think of any others - perhaps EE?
I took an O2 free trial BB offer myself a few years ago, but that was ADSL MAX and I had the line rental with BT Retail so with a MAC it was no problem to migrate to another ISP before the end of the 30 days...
For most people the Sky 30 day trial works out because most people choosing Sky are looking at mass market providers. So those unhappy with Sky will simply switch to BT or TT and will get a free install. Very few use Sky and then think 'this doesn't work too well, best give UKFSN a go.' They say 'should have gone with BT' or 'TalkTalk works well for my friend.'
In experience BT definitely have a way of lying about the disadvantages of moving to LLU. When my mother moved from BT to Sky they told her that her telephone number would never work on BT again and would be stuck on Sky forever. They told her Sky cannot beat BTs speed as BT has the monopoly on the market. They also told her Sky would charge her so much more per call that she would regret moving. She almost didn't switch. Ironically she moved houses out of a Sky LLU area and has her old number back with BT.
I think there needs to be a better method of switching between ISPs than currently.