Apple announced last week that you will be able to run only one application at a time on the iPhone. This means you won't be able to have applications that run in the background, maybe keep a connection open to a server and notify you when appropriate.
I see really two classes of applications that will be in great demand:
- Games. Obviously.
- Push applications.
Consider these examples:
- An IM client;
- A Twitter client that notifies you when one of your friends have posted a new message;
- A Podcast application that downloads shows over the air (say at 3 in the morning, so it doesn't bother anyone);
- A New York Times reader, which always have pre-downloaded for you all the latest articles from the New York Times;
- A Skype client, which notifies you when someone is calling you.