BT, Sky and TalkTalk normally insist on you having their line rental. You are probably getting away with it with Sky at the moment because of coming from O2, but you may be able to get the same if you went to their FTTC.
Plusnet will let you have FTTC with your line elsewhere but charge an extra £2.50pm for the broadband. Be wary of their 38MBps package which has only 2Mbps upstream speed, as does the TalkTalk one. That may not be enough to let several people run Netflix, Spotify, catchup TV all at the same time as the upstream needs to feed back that the data is being received OK.
In many cases where you don't take a company's landline their introductory offers aren't available. They only come with the bundle.
How much do you pay the Post Offfice for the line? (Rental, call package, typical chargeable calls). I use my landline very little and pay £13 rental plus £1 caller display. Ordinary calls are 1ppm in peak, 0.8ppm off-peak, with per second billing.
I suggest you also look at Pulse8broadband
at £38 including line rental. (That's who my line rental is with).
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