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Palringo manages to combine the best instant messaging clients into one app for the iPhone. You can load up your buddy lists from your favorite instant messaging services, such as: Windows Live Messenger, Yahoo! Messenger, AOL Instant Messenger, Gadu-Gadu, AOL ICQ, XMPP/Jabber, Google Talk, and iChat. This is on top of the Palringo instant messaging service that includes its own buddy list and a completely user friendly community aspect.
Adding another chat client to Palringo is very easy. You simply select which client you want and let it populate your buddy list. If you have multiple lists from different clients they do mix together depending on who is online and who isn't. This makes things mildly confusing at times, but considering how smooth it scrolls, you shouldn't run into any issues.
If you're looking for more of a chatroom type feel you can easily join or create a Palringo community. This populates a portion of your buddy list with a Palringo users who share the same interests as you. Each community has its own main chat room as well and can be enjoyable to participate in if you're looking to talk with new people.
Unless you're only looking to use AIM with no intentions of loading up any other form of chat client, Palringo should be your instant messaging app of choice.