Truecaller is a software application that can help you block calls on your wireless phone.
Truecaller has a caller ID that allows you to see the number of who is calling you, allowing you to block calls from telemarketers and others if you wish.
One of the great features of Truecaller is that it uses a crowdsourced directory to give you as much information as possible about the number that is calling you, even if it normally would show up as unknown.
Truecaller is free and safe to use on your Android phone, although the download process is a bit more complex than with other phone apps. But it is well worth the time to download it to help you keep spammers and telemarketers at bay.