This number must be registered to carphonewarehouse because I am a customer of theirs and from the other posts on here, every company that has been mentioned (AOL Broadband, Talk Talk etc) is owned by them. I have never answered it because I didnt like the fact that there was 12 digits in the phone number.
Someone said that the number is registered to south africa. not surprising since as there are thousands of british based companies that have call centres out there.
As for it asking for you to hold while someone becomes available when they have rung you, this will be because your numbers are in a predictive dialler. This basically means a computer is constantly ringing a massive list of telephone numbers and when someone answers, it puts it through to an available agent. But if you answer and no-one is available at that time then you will be asked to hold until an agent becomes available to try and sell you something!
As annoying as it is, as far as i know the only ofcom rules with regards to outbound diallers is that they have to leave a telephone number so that people do not receive annonymous calls. If you do answer it, simply ask for them to remove your details from their campaign list and they should do it for you.