Facebook is my most frequently used app. I love Facebook for letting me stay in touch with my friends. It keeps me up to date about my friends’ thoughts, news and relations. Fortunately most of my friends are using Facebook for their personal life, because that’s what I am really interested in. Facebook is also a very casual way to get to know new people in my life, which are very common lately. The Facebook app is — in my opinion — the best mobile implementation of a social network.
iPod
This is simple: I am listening to music all the time.
Messages/WhatsApp
I prefer to use WhatsApp, because it’s free, but I am using both apps with the same priorities and principles. I treat incoming messages with a higher priority than Facebook notifications or classic mail. It’s very likely that I reply instantly, if there aren’t more urgent things are going on.
Reeder
I use Reeder to stay up to date with professional stuff. I am subscribed to many rails-related, usability and design websites/blogs, which I usually check every morning in bed or during breakfast. I chose Reeder, because it’s really easy to use, yet powerful. Did I mention the user interface is very beautiful as well?
E-Mails
I deal with incoming mail in a very special way. Professional as well as personal mail. The default mail client helps me applying the Inbox Zero principles while not being feature overloaded. The only thing I don’t like is, that I am unable to hide the unread mail amount badge.
These five (or six) apps seem to be important for me. In many situations I notice missing them very much. That’s why I am going to get a new one as soon as possible. If you're used to (use) an iPhone - life sucks without it.