I've been using iChat to send text messages for a while, but disliked the fact that I had to have two contacts on my buddy list -- one for their AIM/.Mac account and another for their mobile number. While playing around today I tried something new and was surprised with what I found.

I went to my friend's Address Book contact and created a new AIM account with his mobile number using the specified format (+1, then the area code and phone number without any other characters (+13031234567)). I then switched to iChat and proceeded to press the + symbol and add my friend (again) to my buddy list, making sure I selected the new AIM account with the mobile number.

Now, I can see my friend and chat with him when he's online as normal, but when he logs off, his status changes to the color gray and a symbol similar to Apple's WiFi symbol shows up next to his name. This tells me that he is offline, but I can send him a text message using iChat. In the iChat documentation, it says that to send a text message, you have to go to File > Send SMS and type the mobile number in the +1number format, but it says nothing of this capability.