iPhones already exist in the enterprise space. They aren't going to need to buy more of them to use them as laptops, just keep buying the ones they're already buying and use them for two things instead of one.
iPhones aren't being used for anything more than trivial tasks, they are used for phone calls, reading email and light web browsing. Any smartphone can do that, and if we see convergence then probably all the new converged devices will be fine for that purpose too.
It is going to be a lot harder for iPhones to become capable of taking over the job of a Windows PC than for a small Wintel phone to fill in the job of an iPhone.
If convergence devices do appear in the enterprise I think its more likely that the popular ones will be Windows, Android or at an outside chance Ubuntu - and the devices more likely to disappear are the ones not best suited to the desktop work.
I don't think you've been following what industry has been doing with iPhones.
First of all, "light browsing, reading, and phone calls"? You clearly haven't been in sales. Entire 2000 word screens are usually banged out on one's iPhone or Blackberry. The calendar app has to manage hundreds of events, etc.
I do almost all of my browsing on an iPhone.
Airline mechanics at at lesat one major global airline have been using them to log their maintenance activities with precise detail.
More than one Class-1 railroad is prototyping iPhones and iPads for crew and yard devices to manage train manifests and marshalling orders.
Doctors are using their iPhones for looking up and editing EHRs in some hospitals.
Everywhere I look in the enterprise, they are killing the PC in favor of the smartphone -- today.
Again, that may be important work but it is all very basic work that can easily be done with any mid-range phone or tablet. Historically there may have been genuine reasons to pick the Apple product, but as time goes by there is less and less reason to choose Apple, and more and more reason to choose one of their competitors.
For "real" office work that needs a convergence device, Apple is in even less of a strong position, for the reasons outlined elsewhere.
They are likely to find some niche applications, and probably do well in the consumer side, but its hard to imagine Apple having much success as a PC replacement (and decreasing success in the long run as a BlackBerry replacement)
iPhones already exist in the enterprise space. They aren't going to need to buy more of them to use them as laptops, just keep buying the ones they're already buying and use them for two things instead of one.