Yea...
As things sit right now, that is really not that much of a possibility.
First, the iPhone only supports the Bluetooth Headset Profile.
(No file transfers over bluetooth).
Secondly, one would need to create their own SMS app that allowed them to both send and receive whatever they please from another source. At this time, the iPhone SMS app does not support terminal input, so no automation is possible at this point.
Sorry, maybe the SDK will make your life a little happier!
Personally, I would rather just have the ability to use SMS.app in Landscape. Either that or just have a smaller font for my conversations as I get a few that get a little on the long side.
The widescreen keyboard on SMS would definitely be nice, too!