(T-Mobile Photo Via YouTube)

After months of testing with tens of thousands of mobile guinea pigs, T-Mobile today announced a May 31 debut for Digits, a new technology that lets customers use the same phone number across a variety of internet-connected devices as well as add multiple numbers to one phone.

T-Mobile also revealed a crucial detail that it didn’t discuss when it first announced the service back in December: price. T-Mobile COO Mike Sievert said users can put their phone number on multiple phones or devices for free, the company’s “favorite price.” Adding a second number to a phone will cost $10 a month, but for a limited time, customers on the latest T-Mobile One plan with the $5 monthly Plus add-on will get that second number free.

All T-Mobile customers will automatically be upgraded to Digits. The company says Digits will work with any device, from smartphones and tablets to computers and smart watches, and even old-school flip phones. Digits works across multiple carriers like AT&T and Verizon, and users can also log in on various internet browsers.

Once users put their number on a device, they will be able to access calls, texts and voicemails the same way they can jump around with emails and programs like Google Hangouts and Facebook Messenger. That also means when someone calls, all devices will go off in a cacophony of notification.

T-Mobile COO Mike Sievert

“This is a complete change in how the network thinks about routing calls and messages,” Sievert said. “Now, for the first time ever, instead of being based on data that’s seared permanently into that little SIM chip, never to be changed, it’s based on your identity, which means any device that you add your identity to can now receive your calls and messages, natively from the network.”

Through testing the service, T-Mobile said it learned how customers most want to use Digits. One of the most popular functions was the ability to text from PCs, but users also favored a variety of specific uses for the service.

T-Mobile said more than 30 million people carry at least two devices — a personal phone and a work phone, for example. Digits lets people put their personal and professional lines on the same phone. It could also help businesses move to a mobile-first model, where a business’ central number can go to multiple employee phones rather than a landline.

T-Mobile said Digits is also a good fit for those who want multiple devices for specific situations — such as a small, rugged phone for outdoor adventures, a big tablet for travel and a smartphone for business.

Sievert called Digits the 21st century answer for the landline. But there are still plenty of landlines out there — 58 million, according to T-Mobile — and many users in the Digits testing program said they would happily cut that cord if they could keep the shared number.

T-Mobile says Digits is a good option for people have to put their number out there to a lot of strangers, such as an eBay seller, or someone using online dating websites. If something goes south it is easy for a Digits user to change that second number without disrupting their business or personal lives.

“If you ever want to cancel or change out your second set of Digits for a new number for any reason and ghost everybody you gave that old set to, we can take care of that for you,” Sievert said.

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