How would you trigger the need to play the announcement? Security? Are you stating that some person would manually start the pre-recorded message? If that's the case, you could hook up the sound card of a PC in security to an analog phone via a Plantronix MX-10 hedset amplifier, use Vox Studio 3 (software:
http://www.xentec.be/download/download.html) to record both the DTMF tones to access the paging TAC and Zone(s) and the announcement itself into a wave file. The security personnel would then take the analog phone off hook and execute the .WAV file.
I use Vox Studio 3 in demo mode to record DTMF tones for auto-attendant *T transfers into .wav files and ftp to VAL, but it's intended purpose is to "allow rapid recording and editing of thousands of voice files using a Windows PC equipped with a standard sound card." Sounds like just the ticket.