Switching is a bit painful
I've done it a few time with mobile ops and ISPs and only once has it been smooth and all I lost was a few hours connection time.
Often it is difficult to compare like for like charges, Halfmad has a good example - I found for ISPs/broadband I had to consider line rental which I pay yearly up front but which is not cancellable (normally) and then whether to move my phone as well and whether I could get a similar call plan, so I suspect all these things hold people back.
Biting the hand that feeds IT
