If a building is only as good as its foundation, then a smartphone is only as good as its app store. Even as manufacturers continue to stack their handsets with YouTube support, instant messaging, and other essentials right out of the box, the features just don't add up to the amount of capability a phone can take on in the hands of the right developers: You name it, a good smartphone can do it. The app store you buy into will have a longstanding effect on the way you use your phone - perhaps more than any other feature. But it's tough to get a feel for every smartphone app store when you don't get to push a cart down the aisles until you have a carrier contract in your filing cabinet and there's no turning back. With that in mind, we've gone out and done the legwork for you and compiled a dossier on five of the most popular (and populated) app stores out there. So check out the wares, do your research, and invest wisely, so you know which is worth dialing into.