I\'m doing research for making a chat based app for the iPhone (it\'s not really text chat in the regular sense, but the principles are the same).
Maximum 6 people
In my opinion the best solution is socket, but you say that you can't implement the server side for this.
You could also implement it with push notifications. You can receive the push also when your app is running and send all the data you need inside the push. Usually chat messages are short...
If you don't want to mess with push notifications on the server then the only thing left, as long as I know, is the polling.