There is a program called "FlusiFix-2004", it just doesn't only add callouts, you can control everything with it, everything which has to do with FS9. But I'm not shure if there is an English version of this awesome lil help program, you can find it here
. If you enter the site, just click on "FlusiFix-2004" on the left navigation menu under "Flugsimulator 9". Then you scroll down and there is a link "Download", there you click on... It's a great allround program.