If I was in the mood, I would have a lot of fun with the idiots claiming to be with Microsoft. They would start reading from their script about how they needed codes from my computer so they could do the updates. I would inform the person that I do not have a computer. This would completely escape the person and he or she would keep reading from the script. I would politely inform the person a second time that I do not own a computer. Finally, the person would realize what I just said and the ask "you don't own a computer?" I would respond by saying "for the third time now, I do not own a computer". They would very quickly get off of the line at that point or just hang up. I don't get calls from these guys anymore.
Unfortunately, whatever their scam is, they get enough people to fall for it; otherwise, they wouldn't be bothering. The other unfortunate problem is that no matter what law or regulation is passed there will always be a way to get around the intent. Our legislature had a bill before it the other day to ban robocalls and some legitimate businesses (the utilities specifically) complained that they use the technology as a way to remind customers that they are behind in their bills. So this bill will go nowhere.
If we don't recognize the number either on the landline or the cellphone, we let it go to voicemail. No one ever leaves a message, but it is an inconvenience to have to get up and pick up the phone to see who is calling.