Sometimes you will receive phone calls from people on your cell phone and not ever know who it is, as their name doesn't show up on caller ID. You can figure out who this person was who called you in a number of different ways, depending on how far you want to go to figure it out and what they are doing when they call you.
As with many things you can put into a search bar on the Internet, putting in a cell phone number is no different. Sometimes a lot of information will come up on it, so there it is worth a shot, as it is easy, free and harmless. At the very least, you will know the area code where the cellular call originated from and can probably track down the region based on the first few numbers in the seven digit code. While cell phone numbers can obviously travel, this may give you a clue as to wh was calling you based on where they set up the cell phone.
Reverse Cell Phone Look-Up
There are sites on the Internet which will lookup cell phone records for you if you enter in the number of the phone which called you. While the initial search to gather the information is free and will see if there are records or listed information the company can find on that cell phone number, the delivery of the actual records will cost a varying amount of money, depending on how many records there are and how much information you want. This method also falls into a legal grey area these days, so be wary of gathering these records and using them to prove anything in a court of law.
Private Investigators or Police
If whoever is calling you from the anonymous number is harassing you or is threatening you, then a private investigator can be hired for a fee to figure out who it is who is calling you, or the whole issue can be turned over to the police. The police department can easily look up who the person is who is calling you as they have the authority to do so and while this information may not ever be able to be used in a court of law, it will point you and them in the right direction as to the motive of whoever is calling and bothering you.