2 phone numbers to 1 line.

[#1]

I have two phones in our house.
1) Residential phone line, under BT control, arrives into the house in the kitchen/dining room.
2) Residential phone line, under plusnet control, with fibre broadband connected. Arrives into the house in a study room
(there is no master sock for either of these, it appears in BT's wisdom, they routed the phone cables straight into the attic when installing them 30 years ago)
The reason for the two lines is that I had internet long before broadband was ever heard of (I was in fact in the first batch of demon customers back in 1992), so you needed a dedicated phone line for the internet....and then it went to ISDN2...and then ADSL....and now fibre. This line was never used for voice calls.
So now I really only need 1 phone line, to provide both voice and broadband. Obviously, the number that everyone knows how to contact us, is the residential BT line.
Ideally, I want the broadband to continue as it is now, as it is appropriate to have the router / modem etc in the study room.  However I'd like to move the residential phone number to this line, and thus get rid of the unnecessary line. In other words, I want to end up with a single line, from plusnet, that has our (currently under BT) residential phone number on it, and also the (plusnet) broadband on it, on the physical phone line that arrives in my study. I can then use wireless phones to get phone capability back to the kitchen/dining room.
Is there any way to achieve the above, without losing either phone or broadband service for an extended period ?

[#2]

Requests of this ilk have in the past been sorted by the "house moves" team... though this is a complicated one!
...transfer existing BT phone line NUMBER to PN without BB
...cease existing PN phone line NUMBER but keep BB
...move 'migrated number' to existing line
Might be easier to ask for
...BB service to be moved to BT phone line / number
...cease PN number
...migrate BT phone number to PN
...ask for the drop / tail to be relocated to the present location

[#3]

Could it not be done as a cease to the BT line, and then a renumber on the Plusnet line to the one from the BT line?
I was talking about doing something similar, though a renumber of a line, then porting the original number to VOIP, and I think it was James Bailey said it should be possible.
Phil

[#4]

The low-risk solution, which I would follow, is to transfer the BT line to PN (assuming you want to pay them for your phone) then take out a new PlusNet broadband contract on that line.
You'd probably be able to get a new customer deal AND a referral discount.
When it's all working downgrade the current service to a "dial-up" account (to continue to get referral payments), terminating the PN broadband (yes there will be a termination charge) then terminate the line.
Rework the wiring in and from the loft as appropriate. DIY or ask for the line to be "regularised" if there's no master socket, which should be done free by BT (on behalf of your ISP) and they should put a master on one of the existing extension cables, as nominated by you.
I take it as you're paying for 2 lines at present that any short-term costs to sort this out are not really a major factor.  

[#5]

Hi tangey,
Thank you for your time on the phone today.
As we discussed please get back to me on the personal ticket I've created on your account once you've received confirmation if you're in contract with BT or not and we can take things from there

[#6]

Lynn,
Many thanks for picking up on my message and taking ownership of the issue.
I'll check out the BT contract position and get back to you ASAP. We haven't had need to change the BT contract, so I'm pretty sure I'm out of contract, but I will double check
Regards and Thanks
Ian