All portable electronics are destined to be converged into the mobile phone. That is not to say that there won't still be iPods, GPS navigators, cameras, ebook readers and so on, but our phones will be able to do the same thing well enough that they will swallow up the low end of the market almost automatically. Only if you want really high quality or fine-grained control will you need to buy a dedicated device. For everything else, there's an app for that.
Mokalus of Borg
PS - And for some things, an app is the only time such functions have been feasible.
PPS - That's the extreme low end of the market where it's not worth making dedicated hardware.