I do not believe the Dect 6.0 phone model cs6319-2 that you have given supports answering message service (internal voice mail).
There is no mention of any such feature in the user manual.
http://www.vtechcanada.com/support_docs/vtt/CS/CS6319_en_cib.pdf
In case your model number is not correct and you believe the phone you have has answering system you can download this Vtech manual provided your model is searchable on the site.
http://www.vtechphones.com/support/general/manuals