What country are you in, make of phone, network?
US, LG and MetroPCS.
Why does this matter?
Are you currently using this?
If you are then here are some alternatives:
Keep in mind, for any of these blockers, the call still has to hit your cell phone and the app needs to be running in the background to "catch" it. Your phone may still ring briefly while this is happening. Or if android shuts the service down (sleeping, idle etc...) to save battery, the app needs to start the service then snatch the call adding more delay.
I use StitMe to block anonymous communication and spam call blocking guard with instant message, chat messenger and free Voice Call. You can search int on your iTunes or google playI publish my cell number and get a telemarketer at least every hour. I have a call blocker, but I hate it.
Can anyone recommend a good one?
Are you currently using this?