I ported our landline number from Sky to A&A and I will admit the process was absolutely flawless.
My only gripe in my case was that I had to port the number and cease the broadband at the same time, but at the time I had 2 x FTTC circuits so I was able to do that and be without one lot of internet for a while.
But, the number is now on VoIP and works well.