In a perfect world, we would throw our cellular phones away and move as fast as possible to an all Internet wireless system, using VoIP to make phone calls and the same packet-based IP transport for all other kinds of data--one kind of transport system for everything--voice, video, Web, you name it.
But infrastructure usually trumps good ideas. We already have a vast cellular infrastructure that works pretty well, at the expense of having a separate wireless road system for phone calls--one that does not work with the more versatile Internet road system. And it is hard to imagine how you just throw away all the billions already invested and invest billions more for a new wireless Internet everywhere.
But the cellphone manufacturers may have cracked this problem with UMA, or [link no longer available] Unlicensed Mobile Access. Using a single wireless phone, users can use it to make calls when near a WiFi hotspot OR on the conventional cellular system. Even more interesting, you can do so seamlessly. You can start a call on the cellular network, walk into a WiFi hotspot, and the phone will switch to the Internet seamlessly while you are talking.
There are a lot of issues to be worked out, including pricing (it's cheaper to carry voice calls over WiFi/Internet), but it gives the cellular companies a roadmap for making the transition to an all Internet road system gracefully. We'll see more and more phones coming standard with WiFi, which will also make it easier to use our phones and PDAs to check mail, surf the Web, watch movies, and stream music.