Whether a product is "finished" or not, it is really difficult to define and very much rest on the expectation of the user. IMHO, iPhone and others are phone with Interactive kiosk features, while the N900 is a general purpose computer with a cell phone module, gps module and camera attached.

So with a "kiosk", you are limited to offerings of what the manufacturer/vendors would give you. Your expectation is highly "managed" and, in theory, overall user experience would be and should be good to worry-free.

With a general purpose computer, you are the master of your domain() -- in the other word, the built-in "features" can be basic or even bad(depending user expectation). However, you are the Master after all, so there is ,in theory, nothing to stop you from making it(ie. the 'must'-have feature in your book) better. You can add the feature you want(limited by the hardware and your skill, of course). It will require effort and time from the user to yield the best experience and functions.

Note that I use a number of 'in theory' in my rant above, so the truth in everyday usage is somewhere in the middle not 100% black or 100% white

Cheers,