In many cases, you can't have two phones with one number assigned by your phone company. However, you can often use call forwarding to send calls made to one number to another, and you can use services that will route calls to multiple phones. You can also have two phones with the same SIM card passed back and forth to share the number between them. Some phone companies do offer services to have one phone number shared with multiple devices, so check to see if yours is one of them.
Two Phones and One Number
There are times when it is useful to have a call to one number ring multiple phones. For example, you might have a business run by multiple people and want to have calls to the business line ring multiple individual cell or landline phones. You might also want to receive personal calls on both your cellphone and your home or office landline or receive calls on your home phone at your cellphone when you're not there.
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Unfortunately, you often cannot have multiple phones with the same number. Many phone companies simply don't support it. One exception is a product called Verizon Number Share, which lets you receive calls on multiple devices, but it mostly supports wearable devices like smartwatches rather than additional phones.
T-Mobile also offers a service called T-Mobile DIGITS that will allow you to share a number across multiple devices, including phones, watches, tablets and computers. If you're a T-Mobile customer, you can use the T-Mobile website or app to set up the service. Contact T-Mobile if you have questions about how to use DIGITS.
Check with your cellphone provider to see if such a service is available.
Using Call Forwarding
Many phone companies also provide call forwarding services. This service allows you to have incoming calls from one number routed to another number. You usually can't use call forwarding to make calls from one phone number appear to be coming from another number.
You can often configure call forwarding to either route calls immediately from one number to another or only do so after you fail to answer after a certain number of rings. Check with your phone company to see what options are available, how to set up the service and whether there's any cost involved.
Moving a SIM Card
If you have a cellphone with a SIM card, you can often move the card to another phone compatible with your carrier to use that phone to make calls. A SIM card is a small plastic chip that stores information about your cellphone account.
There are several types of SIM cards, and not all phones are compatible with all cards and with all carriers, so make sure that your devices and cards are compatible. Contact your carrier with questions.
Remember that the SIM card will only be present in one phone at a time, so make sure that's the phone you have with you when you want to make or receive calls using that particular number.
Using a Third-Party Service
Some third-party services allow you to sign up for a phone number and have it ring multiple phones. Smartphone apps often allow you to use this number to make calls from those phones as well and you may be able to make calls and send texts from other devices, like computers and tablets.
Some services that offer this capability include Google Voice, Burner and TextFree. Each of these services offers slightly different options at different price points. Shop around for one that offers the level of service you need at a price you like.