It depends on who your Internet provider is
At my previous property I had no choice about the BT Landline, as there was no alternative in order to obtain dialup and then broadband
However, at my current property phone and Broadband are separate (TeleWest, now Virgin Media)
My first years contract was cheaper with phone line, but I rarely used it
I then removed the phone line from the rolling contract and use mobile phone only
Whilst this has reduced my annual costs this does present some small issues where some companies require a landline and won't accept a mobile phone, but that is their loss
As an example, every year I compare my electric costs
This year it worked out slightly cheaper to move to another provider
However, during the appication process my mobile phone number was rejected
I then phoned them up and was advised they could only accept new customes with a BT Landline
I then pointed out I was a Virgin Media customer, and they corrected this with a Landline from any provider
I then phoned up my current electric provider and they agreed to match that offer, by way of an adjusted online discount
Mobile phone costs are slightly higher, but if you terminate the landline this in effect releases at least £10 per month, and this pretty much offsets that higher cost