I used to adore all-in-one gadgets, but not anymore. Smartphones, more than any other gadgets, are getting more and more all-inclusive. In my opinion, however, some applications are more practical to purchase as standalone gadgets.
Take the GPS, for example. You might be tempted to overspend on a new smartphone, just because it has a built-in GPS. The app itself might be free or costs very little, overlooking the fact that you have just ploughed in substantially more money than you otherwise needed to. Have you considered that such a built-in app is single-user only? Someone might occasionally need to borrow your "GPS", but he or she cannot do so without taking away your phone as well.
What about the built-in e-reader function? No thanks, I'll stick to my Kindle. It has all the book reading buttons in the right places (e.g. page turn, quick dictionary access) which makes reading pleasurable indeed. A smartphone with a built-in reader just doesn't cut for me. The screen is too small, for one. Plus I cannot leave it around for other people to use when I am not using it; I have a daily newspaper download. Again, single-user function.
In fact, all apps on the smartphone are single-user only. So if you are considering buying a cutting edge new smartphone, you might be better off getting a non-phone gadget (like iPod Touch) to use separately from the phone. Believe me, it is more practical. Steve Jobs probably knows it, which is why the iPad doesn't double as a mobile phone.