How to change the voice on an old Radio shack 900MHz phone?

I have this old cordless phone made before Radio shack started using Unidens. The only info I have is this: it's 900MHz cordless, the serial number is 06010949 and above the serial number is some numbers that are 02H00. I can't see a model number or anything else but that. I need to find a manual or instructions on how to change the message on the machine. A friend gave it to me and helped me change the message with my voice. She has since passed away. Any ideas??How to change the voice on an old Radio shack 900MHz phone?
maybe you could check on google or yahoo search. It might have a site with the manual someplace.

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