That's an interesting side effect. I had thought that you only needed to have an O2 mobile number if you wished to get the discounted broadband package.
I have also discovered that, possibly until the end of the year**, you can't get an O2 broadband service UNLESS the BT line performance database can be accessed.
E.g. if you are on a TalkTalk fully unbundled LLU service O2 can't accept your order.
I'm helping someone with this problem and we can only proceed by ordering a new BT line, waiting for it to be enabled with a confirmed phone number, and then ordering the O2 service.
We'll probably cease the existing line afterwards and they do have the luxury of two concurrent services, albeit at the cost of a second BT line installation.
** I gather from O2's sales department that they hope to remove the LLU restriction just as e.g. Zen are able to do now. I don't know of a confirmed restriction removal date yet.
Kind regards,
Walter