i hardy ever use the bt line in my house for phone calls, i really only have it for broadband. is the time coming now that the connection speeds of mobile broadband are as such that fixed line can be dispensed with entirely for most people?
I wouldn't say that it would never happen, but it's certainly not going to happen soon. Although the technology to achieve high bandwidth through mobile connections exists, in practice it is not commonplace enough to cope with even current demands on bandwidth, let alone future ones.
My phone has great performance over 3G and performance over a tethered connection (for normal web browsing at least) feels pretty much the same as a conventional fixed connection, but all too often (particularly when I'm travelling by train which is when I'd most value mobile internet) it can't get a 3G signal and I'm knocked back down to 2G and a world where nothing except Opera Mini is usable on the phone and you can forget about trying to load real websites through a tethered connection.
Even where a good quality 3G connection exists, the infrastructure to deliver this kind of connection on any great scale simply isn't there, so mobile data is kept expensive in an attempt to reduce the strain on the infrastructure and keep serious internet use firmly away from mobile connections.
Until we reach the day when I can spend the evening on Youtube whilst a ton of stuff from Vuze downloads in the background without needing to take a second job to pay for it I don't see fixed connections going anywhere.