I'm in the UK and mostly work from my home office so robocalls and the like became really annoying. I installed a "trueCall"[1] device and it completely stopped robocallers, those "I'm calling from Windows" scammers (which were actually funny) and others. I just use the basic setting where it tells the caller "Press 3 to be connected. If you are a cold caller please hang up and do not call again". I'm actually a little surprised how effective it is.

If the robocall were to blast DTMF tones down the phone it could automatically bypass and I'd need a more advanced setting (of which there are many). But I haven't needed to do that in over a year of operation. Only downside so far is my bank has recently taken to calling me up to verify transactions, using a robocaller, so I may need to give them my mobile.

I considered setting up asterisk to do something similar since the device was a little pricey, but decided the time saving was worth it. It also records my calls to a SD card if needed. Now my land line is the disposable one I give out and my mobile number is the one I'm careful with.

Not affiliated with them, just a satisfied user.

[1] http://www.truecall.co.uk/