How to research an unknown telephone number

A guide on how to research an unknown call number.

Symbol image for unknown call number.
Illustration: Noto Emoji. Composition: Gionathan Diani.

Phone book and directory assistance services.

As a first stop try the White and Yellow Pages aka phone book. On the website of OFCOM a list of directory enquiry services is available. If the phone number is not found replace the last or last two digits with a *, which can be used to check if the number could be a direct dialing-in number. A quick survey among friends and family may lead to the goal.

Search with web search engine

Under certain circumstances, the phone number has been published on a website, for example of a club or a company. To do this, perform an exact search with a search engine. An exact search can be done in most search engines by putting the search term in quotation marks, e.g. “031 123 45 68”. The published number could be written in any format, therefore vary the spelling of the phone number e.g. with an international prefix “+41 31 123 45 68” or without spaces “0311234567”.

Search on platforms

Phone numbers can be deposited on platforms such as Facebook, LinkedIn or Xing. If the person has made (or neglected to make) the appropriate settings, you will find her.

Profile picture in messenger app

The profile picture in an instant messaging service may help to determine the identity behind the number. To do this, save the number to the address book so that it shows up among the contacts in an instant messaging app like WhatsApp, Telegram or Signal. If viewing the profile picture does not provide any clarification, save the picture and perform a reverse image search. Search engines for image reverse search include Pixsy, TinEye, Google, or Yandex.


If the previous steps did not lead to success, there is still the possibility to return the call. However, caution is advised here. There are numbers whom are charged. Tips on how to protect yourself against unwanted calls can be found on the consumer protection (german) website. The instructions are also suitable for checking whether your own phone number is unintentionally publicly accessible.