I want to create a chat sort of application on the iphone. I know how I would go about implementing a poll model, where the iphone would poll the server to see if any messages have arrived and if they have it can retrieve them and show them to the user. However im more intersted in a push model, where the server pushes new messages to the iphone and it displays it to the user. The part im having a hard time figuring out is how to go about opening some permanent connection on the phone that will listen for incoming messages...Any suggestions or comments would be appriciated..
Thanks
Daniel
The iPhone 3 SDK has push support built in. Basically, all messages that need to be pushed (from all apps) go to Apple's server, which maintains a persistent connection to the user's iphone. The upside is that you dont have to worry about it and your app can get updates even when its not running (so like, from the home screen). The downside is that your data has to go through Apple's server.
来源：https://stackoverflow.com/questions/1375645/iphone-creating-a-chat-application