Many years ago, "convergence" meant voice+data. Everyone assumed that you'd have one network, one device, unified messaging etc.
I used to speak at a lot of conferences saying that convergence wasn't that simple. What happens is that underlying enabling technologies converge - chips, screens, memory, software, network protocols and so on. Inevitably, someone jumps to the conclusion that just because you can put all this stuff in one device / network / application / service, people will want it.
These "visionaries" then completely ignore the fact that the new scale-economies from all this "enabler convergence" also means it suddenly becomes much cheaper and easier to make "divergent" single-use products as well. Most "all in one" jack-of-all-trade alternatives are usually "master of none".
I used to illustrate this point with a picture of a toaster and a washing machine. Both use a "converged" electricity supply. It's entirely possible to equip your kitchen with a single converged toaster-washer, but why would anybody want one? Even with personal items, convergence isn't important. We could have had combined watch+wallet years ago. Sunglasses+hairband. Trousers with built-in belts. All feasible examples of convergence, but completely useless.
The same is true with mobile devices. "The MP3 player is dead" "Standalone digital cameras on the decline". A single converged device for everything! Yeah right.
My prediction: in the future, the average person will both own, and carry, more devices that they have today. And they'll have ever more ways to be contacted - multiple phone #'s, IM accounts, email addresses etc. It's interesting that some operators are now openly pitching the idea of customers having two or more phones. While others give away free iPods with a new handset.
Sure, some functions will get absorbed into other devices. But it'll be one step forward, two steps back. Standalone devices will always exist, and always be desirable. Why should I wait until I renew my phone contract to get a better digital camera? Why would I want my upgrade cycles for my games machine & my mobile web browsing gizmo to be in sync?
I'm fed up with Nokia & other companies saying "we're the leading MP3 player supplier". Maybe, but what proportion of them get used? You're probably the leading infra-red device vendor too, but you don't make a big song & dance about that, do you?
Most telling was my visit to Korea last November. As far as I could see, everyone had a really cool and capable cellphone. And a really cool & capable MP3 player. And a really cool & capable digital camera. And fast broadband & cool & capable PC at home. In the most advanced mobile market in the world, there are shops everywhere that just sell standalone MP3 players - 100s of varieties of them.
So remember..... divergence is the future.