For which Phpbb version? I did something similar to this for 3.1 but I had to hardcode it in myself. Doesn't save to the database, but information is posted in the beginning of the OP and retains when you preview post as well. I believe I took the support ticket extension, and I modified it to have the type and number of forums I wanted with whatever information I wanted in them.
I am a web developer/administrator, specializing in forums. If you have work you need done or are too lazy to do, pm me!