I didn't actually do a reg edit to move the text messages to internal storage, I just deleted mine and freed memory. I'm sure there is one. I think I read a thread with a regedit to move all email messages to internal storage, not just attachments. Since text messsages are in the windows/messaging folder, I suspect all messages, email and text and even picturemail are in storage memory. looks like this thread has the necessary regedit,
http://forum.xda-developers.com/showthread.php?t=298646
I haven't actually done any reg edits yet, but now that I see this and just found this other post
http://forum.ppcgeeks.com/showthread...=most+complete I'm really tempted to try some!