No Caller ID: How to Block "No Caller ID" and Other Unknown Calls on Your iPhone
Are you sick of having your family dinner interrupted every night by an automated "free vacation" offering? Getting mysterious "No Caller ID" calls day in and day out?
There is a way to stop this on your iPhone - you just need to be prepared to not receive any calls from numbers that aren't on your contact list!
In five easy steps you can send all those mystery calls to your voicemail to check at a later time.
Are you ready?
Tap "Settings" icon from your iPhone's home screen.
Tap "Do Not Disturb."
Slide "Manual" toggle on.
Tap "Allow Calls From."
Tap "All Contacts" under "Groups."
After following these five steps, press the Home button. Now you won't be alerted to unknown calls on your iPhone. Don't forget to check your missed calls every once and a while, though. You don't want to miss anything important.
Please note that this trick won't block the calls, but only silence them and let them go to voicemail, leaving you undisturbed. Afterwards you can run any missed calls you had through a reverse phone lookup app, like CallerSmart's community phone book, to see if you should call back or just block them.