I couple of years back I worked on a project to replace 17,000 landlines across the BBC (primarily TV Centre and Broadcasting House sites) with Skype. Not that there were 17,000 employees but there were that number of landlines scattered all over the place and they cost a packet to maintain and run. But they kept a very small number of fixed landlines separate from the main telephony/internet access lines, as it is essential for the BBC to have resilient communications in the event of complete loss of internet access and/or mobile telephony as could happen if the Service providers and their networks were taken out. So landlines will have a place until 'mobile' telephony is a lot more resilient than it currently is.