Here is how you can send and SMS or "Text Message" to a mobile phone. This works on Verizon, Cingular/AT&T and T-Mobile for sure. It might work with other carriers, but I'm not sure. For this demonstration, I will be using iChat but I'm sure you can use other clients as well.
It's a pretty simple process.
I thought this was pretty interesting and useful, I hope you do too. Enjoy :]
It seems that with the new iChat they specifically incorporated the feature of sending to SMS. Now, all you need to do is push Command+Option+N and you are presented with a nice little window titled "Send SMS." Just enter the phone number of the person you wish to chat with and your message will be sent directly to their phone as mentined above.