I guess so but I loathe voicemail more than I loathe the occasional marketing call.
It's easier to just answer given the overall chance of it being a waste of time.
Just let your voicemail fill up, if it bothers you that much. If you miss an important call, it will show up as a missed call on your phone.
This is getting really off topic but I also don't answer calls unless I know them. My mobile voicemail is redirected to my Google Voice # and the automatic transcription is good enough that I usually don't need to listen to the actual voicemail. You might want to give that a try.
No Google Voice outside the US and I've never found a satisfactory alternative.