Re: Stop using landlines.
Firstly my wife's mobile get loads of these shit calls, fortunately mines currently get few, but for how long?
Secondly living without a landline rather depends on where you live and other factors in your environment. Vodafone's signal round here is crap these days whereas it used to be quite good, a little way down the road the is a hole where no-ones mobile signal works. My office at home seemingly has magic glass that cuts off the signal on all the networks. I can damn near see an O2 mast, open the door - 5bars, shut the door 1 on a good day.
As for relying on VoIP, not sure how that solves any of the problems since you still have a phone number the bastards can hook onto. But even with a pair of bonded ADSL lines the reliability is no where near good enough if you NEED to be in contact with the world. I have the landlines connected up as a backup for the VoIP phones.
Besides with no landlines there would be no Internet connection. 3G or 4G doesn't cut it I'm afraid, have that as a backup with a proper external antenna attached to the router but latency times are much longer than the ADSL and while peak bandwidth might be OK, it rather depends on who else is working locally. No "cable" here since the stupid cable companies tried to get the builders to pay them to fit the wiring, when at the same time they were digging up half the country and laying string down the holes for free, so no other way of getting online.
And I'm lucky, try living outside of towns/cities and people are in a much worse situation.