John - The VTech CS5119-16 can already work by itself. You just need to connect it on the same line where your existing phone is plugged in. They will work as extension phones but features are not shared. You can also add the handset on an existing system models CS5129 or another CS5119. For more details, you can contact our Customer Support at 1-800-595-9511. We are open from 9:00 AM to 3:00 PM, Mondays through Fridays.
Thank you,
-VTech Support
3 years ago
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Posted by:
VTech Baby Monitors Team