Pidgin (or any AIM client for that matter) can send text messages. It's not Pidgin doing the work, but oscar.aol.com (the AIM gateway). To send text messages from Pidgin, add the phone number (+12125555555) where the "+1" is the Country Code (+1 is US) as a buddy to your list. Then send text messages to this newly added buddy.

Not much to it, but it's a nice feature. I use it for "IM'ing" my wife.