If you receive a text message or a call and don't recognize the number, you can use ordinary search engines or specialized phone number directories to attempt to find out who texted you. If you are receiving unwanted contact from a phone number, you can block it on your phone or contact your phone company for help. Keep in mind that caller ID can be faked. If you're receiving threats or harassing messages, consider asking the police for help.
Finding a Phone Number
If you get a text from a phone number you don't have in your contacts or otherwise recognize, and don't want to text back to inquire who sent the message, you can do some online research to attempt to find out who owns the number.
You can type the number into an ordinary search engine such as Google or Bing to see if the number pops up on any business or personal websites that might indicate who owns it. If the number is being used to send scam messages, you may also come across reports of that on various forums and complaint sites when you do your search.
If a typical search engine doesn't provide a clear answer, you can also try typing the number into the search field of a social media site such as Facebook or LinkedIn to see if it's associated with a user profile. See if the name that appears is familiar to you.
Phone Number Reverse Lookup Tools
Traditional phone directories let you type in or otherwise look up a person's name to find a phone number associated with it. Reverse lookup directories let you search for a phone number to find people and businesses associated with it.
Some popular ones online include Whitepages and ZabaSearch. If you encounter a phone number you're not familiar with, you can type it into one of these services for free and see if a name appears. Try multiple people search engines, since they each have different databases, if the first one doesn't give you a useful result.
Blocking Unwanted Calls and Texts
You can block calls and texts from certain numbers on most modern phones.
On an iPhone, tap the (i) button next to a phone number you received a call from or in a text conversation in the Messages app. Tap the phone number again if needed, and then scroll to the bottom of the menu and tap Block this Caller.
On an Android device, the exact steps vary slightly based on your phone manufacturer, but you can usually block messages through your messaging app. Check your phone's documentation for the exact steps if you can't see how to do so in the app.
You can also contact your phone carrier for help blocking unwanted messages.
Be Wary Caller ID Spoofing
It is possible to fake the number where a call or text comes from. That's typically known as caller ID spoofing. It's also possible to scam phone companies into assigning someone's phone number to another, unauthorized phone or to send text messages or make calls from a stolen phone.
As a result, you should use caution if you receive unwanted calls or texts from an unknown number. Don't assume the person the number is registered to is actually the one contacting you, and resist the impulse to reach out in anger about unsolicited messages.
Handling Harassment or Threats
If you're receiving harassing or threatening texts on your phone, consider contacting your local police. They can work with your phone carrier to research who is behind the messages and ideally help you put a stop to it, potentially prosecuting whoever is sending the messages.
Keep copies of the texts so that you can show them to investigating officers.