It is proper netiquette to refrain from telling people you are calling that you are using VOIP.
Caller Need Not Know For VOIP
There are a lot of things that people may never realize unless you tell them. Using Google Voice should be one of them.
When you make a Google Voice call The person you are speaking with will not know unless you tell them.
Therefore, it good netiquette to refrain from telling people you are speaking with that your number is Voice number.