[alex8022]

I use Mr Number Blocker for this on android. You can whitelist / blacklist specific numbers, and set it to hang up or go to voicemail. There's also a crowdsourcing aspect, where after a certain number of people flag a number as spam, it shows up as "likely spam" when the phone rings. I believe you can have those go straight to voicemail as well.

[pzxc]

You don't need an app. Just add a contact called "SPAM", and set it to go straight to voicemail. Then any spam numbers who call you, just add their number to your SPAM contact.