Keep Annoying Calls at Bay With Reverse Lookup
Reverse Lookup is a handy tool that can help you discover the source of unknown phone calls--and thereby avoid a lot of unnecessary headaches from unwanted callers.
Reverse Lookup works by going through your recent calls list. You click on any unknown number on the list, and the app will determine what available data it has on a particular caller. Reverse Lookup doesn't work on every number, however. Specifically, it won't have any data on calls from unlisted numbers, a cell phones, or sources outside the country. In those cases, though, you still have a number of options. You can save the phone number and click a button that takes you to Google results for that number; and you can send future calls to voicemail. Though I wish Reverse Lookup offered some way to block calls from particular numbers altogether, sending the unwelcome caller directly to voicemail is a simple enough workaround. This is something that your Android phone should already be able to do, but Reverse Lookup does the work for you--entering the number into your contacts, and changing the contact's setting to send it to voicemail. The app also avoids having random weird numbers appear in the middle of your contact list by renaming the contacts things like "zzBLOCKED_unwanted number."
A paid version of Reverse Lookup removes ads, is supposed to offer better UI responsiveness, and features future update priorities. But the free version works well enough that I would recommend using it to deal with unwanted calls.