Few things can be more annoying or even harassing than the constant ringing of your phone from a blocked number or anonymous caller. Being that many numbers instantly pop up on your caller ID, a blocked number usually indicates that the source is either a telemarketer, someone you don't know, or generally from a source you may not wish to talk to. While it may be more difficult to find the true identity of this caller than simply hitting the outdated *69 that may have worked in the past, there are still ways to gain information about the number.
Identify that you have an incoming call from a blocked number. If your phone is ringing and there is no number appearing from you caller ID, your phone may display a message such as Private Number, Unknown Number, or something similar.
Dial *57. You will be linked back to the caller. This works even if the source is outside of the United States.
Equip your phone with an advanced Caller ID service. They work by identifying that you are receiving a call from a blocked number and then disallowing the call to go through until the source offers up their own number or they simply change the ringing sound of the phone.
Subscribe online to a Reverse Phone Detective.
Outfit your phone with a pin number from the phone company to stop incoming calls. You will then keep track of the times these calls occur and report them to your provider who will then contact the unwanted caller and tell them to stop calling you.
If these measures do not stop any harassment, your last resort can be contacting the police and having them handle the situation.
The more advanced services and features to gaining information on blocked numbers are costly and can be an investment themselves.