Can anyone tell me what files I need to install aircraft callsigns on fs2004?

You need edit voicepack by bevelstone productions. There is a link in all of our readme's or here:

http://www.editvoicepack.com/

Read the readme's rather than asking here for help. Not being rude but so many people come here asking for assitance and there isnt always time to answer detailed responses. Just read the very detailed and good readmes in the packages.

Nick