Messaging service within my app

I need to implement a message service into my app that works exactly like this:

1. users register with a nickname within the app
2. they can add contacts (just nicknames) and send them a message by just specifying their nickname
3. they can send a message whenever they want, and the message is stored on a server until when the receiver connects to internet.
4. when a message is received, a push notification is triggered.

So, the messages work pretty much like emails, however instead of using email addresses, we only use usernames. I'm also going to build my own back-end for it.

Which APIs should I use or which 3rd party framework can I use ? And any tip ?

N.B. I need to make it work with iOS 3.0 as well.

and in the future I will develop an Android app, so the nicknames should be unique and I should be able to send messages from iPhone to Android devices within 开发者_运维百科the same app.

thanks

I've successfully used the Three20 library and would recommend giving it a try. It's an open source spin-off originated by the author of the Facebook app. It features a bunch of additional GUI components that might be useful to your project, like a message composer that resembles the one used by Apple's email app.

Also, Three20 features a nice framework for handling navigation within your app. Currently, the biggest drawback seems to be that certain features don't play well with the iPad API.

The answer seems to be Push Notifications