Another note on AppleCare+ is that you can only buy it within 30 days of buying a new iPhone. After that you're out of luck. From the Apple site:
AppleCare+ must be purchased within 30 days of the date you bought your new iPhone. If you did not purchase AppleCare+ with your iPhone, you may purchase it at an Apple Retail Store. To buy AppleCare+ at an Apple Retail Store, a Specialist will first need to verify your iPhone purchase date and confirm that your iPhone has no pre-existing damage.
If you missed the window, it helps to consider is what Apple charges for out-of-warranty repair/replacements; depending on your device and how careful you are with it, you might decide that AppleCare+ is not worth the money anyway:
So if you have a 4S and buy AppleCare+, you spend $99
no matter what, and $148 if you have to replace your phone ($197 if you break it twice in two years). Without it, you'd spend $199, but
only if you need service. For me--someone who is really careful with his devices--I'm comfortable without it, knowing that if I do need non-warranty service, it's only going to cost me around fifty bucks* more than I'd pay if I had AppleCare+. Obviously, it gets more expensive if you manage to need two replacements in two years, but after owning three generations of iPhones I have yet to require any service for any of them.
*Depending on your device. My iPhone 5 would actually be about $80 more to replace outside of warranty, but my iPhone 4 would only cost $1 more than it would if I prepaid for AppleCare+.