Hi and welcome to the site, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.
Initially, the Vtech 15550 User's Guide provide instructions for recording your own announcement (greeting message).
Please click HERE.
The manual is in a Portable Document Format (PDF) file and can be viewed in most web browser. Click on the link to open the file or right click then select “Save As…” to download the file. It would require Adobe Acrobat Reader or equivalent for this purpose.