Five of the six characters in the word "iPhone" refer to the phone feature, but the phone is easily the least important part of my iPhone. Thanks to email and text messages, I make and receive cell phone calls far less today than I did years ago. Phone calls can be important, and thus even though I have my iPhone configured so that almost no apps are allowed to play a sound during a notification, I still allow my iPhone to ring when a call comes in. If it is a call from my wife, a colleague, or someone else important, I want to hear the ring. But because my iPhone makes noise so infrequently, when I receive a nuisance call from a telemarketer or a robo-call, I am far more annoyed than when I receive a spam email. Fortunately, Apple recently made it possible for apps to automatically block phone calls. Since early January, I've been using a free app that AT&T provides to its customers called AT&T Call Protect. (If you are not an AT&T customer, there are similar apps available such as Hiya.) After using this app for over two months, I can enthusiastically recommend it because it does a fine job of blocking, or at least warning of, nuisance calls.
Blocking Calls
The best part of this app is that it automatically blocks calls from entities that it believes to be a nuisance or likely fraudsters. The Call Protect app uses Hiya's list of known phone numbers to block. When a call is automatically blocked, you never even know that the call occurred. Your phone doesn't ring; the call just doesn't come through. However, you can go back and look at the call log in the app to see when calls were blocked.
I see that in late February, there was a week when I received seven calls. Two of the were from real people who I wanted to talk to. Five of them were automatically blocked and never bothered me.
You can tap on an entry in the call log to get more information on the blocked call. If it turns out that it was someone who you wanted to talk to, you can unblock the number so that it won't be blocked in the future. But over the last two months, this app has never blocked a call from a number that I would consider to be legitimate.
Call Warnings
If all that the app did was block known fraudulent calls, that would be enough for me to recommend the app. But even better, if there is a call that the app thinks that you probably don't want but isn't as sure, the call is allowed to ring, but you are given a warning. Instead of just seeing the phone number that is calling you, this app gives you some information on why you probably don't want to answer the call, such as labeling the caller as a telemarketer or suspected spam.
As annoying as it is to get a call on my iPhone from a telemarketer, at least with this app I can know to decline the call immediately.
Temporary Call Block
I haven't used this feature, but I see that the app also offers a Temporary Call Block feature. AT&T says: "Temporary Call Block lets you manually block unwanted calls for 30 days. Use the AT&T Call Protect app to select the callers you want to block. These numbers can be renewed for continued blocking."
Fortunately, I don't have a need for this feature in my life. If you do, that is another reason to use this app.
[UPDATE: PRIVACY
A reader wrote in to note that this app uploads numbers in your iPhone's Contacts to Hiya. This is so that the numbers can be added to a white list of phone numbers that are known legitimate numbers. You can get more information on the privacy implications of Hiya in this post by Glenn Fleishman of Macworld. This seems reasonable to me, but consider this before you use this app.]
Conclusion
AT&T Call Protect works great. It blocks calls from entities that you never want to talk to, warns when you probably don't want to answer the phone, and gives you a log so that you can see exactly what it is doing. I recommend that you use the app.
Click here to get AT&T Call Protect (free): 
