After getting pi33ed off with rebooting the iPhone after the keyboard starts lagging when sending a text I've found a cheap fix.

Not sure why but its related so Safari so all I've done is installed a Terminal, su'd then looked up the process (ps -acx)

Then use kill mobilesafari.app

Job done, iphone back to full speed (including menus, springboard etc)

Hope this helps (if its does please tickle the scales.... :hack: