This post references software that no longer exists, notably the AIM (AOL Instant Messager) service, and cellular plans that are no longer relevant. Nonetheless we are keeping this post up for posterity sake. Long live AIM!

The iPhone 3G is awesome, we all know that, but the rate plans are not necessarily awesome for everyone, and some of the cellular plans may be cost prohibitive for the amount of text messages that you get. Wouldn’t it be great if you could send text messages (SMS) for free with iPhone?

Well guess what, you can get free SMS text messaging on your iPhone by using the AIM protocol. Yes, AOL Instant Messenger!

First you’ll need some kind of AIM client for your iPhone, so you can either download the AIM client for iPhone from the App Store, or even use Meebo.

Here’s the most important part, add a new buddy to your list, but use the full phone number with a + sign in front of it, like so: +18085551212.

The plus sign is crucial because thats what tells the AIM protocol that it is an SMS message.

Now you can SMS any phone on any carrier from your iPhone, without using any SMS messages or without having an SMS message plan!

If you’re confused, check out the screenshot which shows adding a cell phone number in iChat.