Since when did the phone actually stop being useful?
Technology progress is great. Even in the small gains in processor efficiancy or IPC, to quad core mobile phone cpu's. As @jacobdrj summerized quite nicely, some things in Science fiction are just not ment for true consumption. Our board of directors and VP's all think they MUST have video conferences for every meeting now. The phone is not dead. Long live the phone.
There are a few scenarios where this would be actually utilized. The first and formost, will be for tweens and their significant other to tweeny chat, and most likely, 'sexting' live. My wife and I, even when on business trips, would not use this. If we are going to go this extreme to talk to each other, I'll use our high quality web cam to chat.
The second, would be legitmate business conferences, though I'm sure this would be very under utilized. In my enterprise, there are many security concerns with over just what traffic and clients can connect to our internal network, and there would be no way I would allow an silly unsecure phone application to connect to our video conference, as god only knows what other malware apps are on it. While neat, it would have to offer business security, and even then, the support nightmare in troubleshooting when our execs screw around with the damn things....
how is this anything but convenient. it doesn't have to be used...but it is nice to have the option. i'm sure i won't use it often...but if my dad gets a smart-phone, he can talk to my 18 month old son without me having to send him a webcam or make sure it is configured. plus, he can do it from the beach, instead of only when tied to the computer...so you have to plan ahead.
if you don't have the need for it, don't use it. no big deal.