Rooms is an easy to use IRC chat room app for the iPhone that allows you to connect with your favorite channel and the rooms that it offers with relative ease. All you need to do is find your server of choice, then connect to your desired room and your good to go.
If you're not familiar with IRC, it won't be that hard to learn, but you'll have to do so elsewhere. The default server that this app offers is QuakeNet. You'll have to remember to change your username per server as well, which can all be handled in the settings.
Once you're on a server you can pick through the chatrooms and find the one you want to visit. There are options to allow you to not disconnect when your iPhone goes idle, but remember that will suck down more battery. As IRC isn't intensive, it shouldn't be too bad on EDGE. You probably should just avoid fast paced discussions however.
You're going to have to know the right servers to connect to for this app to be enjoyable. But once you've got an idea of where you want to go, it operates like a regular IRC client formatted for the iPhone. There isn't really anything special about it, besides it being an iPhone app, but it does get the job done.