Is the move of first line's number to a second line possible?

[#1]

Hi,
I have two working lines at our property. One is ex-BT and is our main phone number, and is now on a long term contract with TalkTalk with both phone and fibre broadband. The other line is unused, but last use was phone and fibre broadband with PlusNet.
We would like to start again the Plusnet phone and fibre broadband service on the 2nd line. However, in about four months time we wish to end the TalkTalk contract and transfer the TalkTalk phone number over to the PlusNet line. It's like a 'house move',  but just moving the number to another line in the same house.
At the end, we will have an unused first line, and the second line will be our main phone number with a Plusnet phone and fibre broadband package.
Can we do this? Anyone done a similar thing?
Cheers
Mel 

[#2]

Hi Mel
Definitely possible, would need to give notice preferably when signing up so this is actioned when needed.
I'd advise speaking to the provisioning team to get this done 
EDIT: Back on a PC now, can type much easier,
You would need to sign up, get the other line active with a random number, when it comes to transferring the number from TalkTalk there are 2 options.
Import the number from TalkTalk, this will cease(stop) their line on the day the number transfers to the Plusnet line, this is the most common way to retain a number from a non-BT based provider, all of this can be handled by Plusnet
If TalkTalk cease(stop) the line and if your number originally belonged to the BT Network(put your number into here: http://ukphoneinfo.com/ ; this will tell you who the Rangeholder or "owner" of the number is) then 14 days after they cease the line Plusnet can get the number made "Spare" on the BT Network which means it can be applied to your line.
the first option would be my suggestion in this scenario

[#3]

^^ As above, really.
I cannot add much more value to the above comment. 
Matty