AT&T (NYSE:T) and T-Mobile (NASDAQ:TMUS) are on the verge of releasing a new wireless network feature that will allow their customers to use one phone number on multiple devices.

AT&T's calling its new technology NumberSync, and says the first device with the feature will be released soon, with more to come over the holiday season. T-Mobile hasn't said when its version of NumberSync will launch, but told Re/Code last week that it'll be better than AT&T's feature. (I guess we just have to take T-Mobile's word for it for now.)  After AT&T and T-Mobile spilled the beans, Sprint piped up and said that it's "exploring" the idea, but has yet to lay out any specifics publicly.

At face value, the ability to use one phone number across multiple devices may not seem like game-changer, but there are a couple of key reasons why the wireless industry is moving in this direction.

Make way for wearables
One of the most important reasons why carriers would want to add this feature is to make it easier for customers to add wearable devices to their networks. 

On AT&T's consumer blog, Chief Marketing Officer David Christopher wrote that, "This means in the future you'll be able to send and receive texts, as well as make and receive calls, from your tablet or wearable using the same number that your family, friends and colleagues recognize. This will work when your smartphone isn't with you, nearby or even powered on."

While not all wearables have their own cellular connections, it's an inevitable progression for the technology. A handful of smart watches already sport cellular connectivity, like the LG Watch Urbane 2nd Edition, and more are on the way.


These Urbane 2nd Edition smart watches boast LTE connections. Source: LG.

By 2020, tech companies will ship an estimated 155 million wearable devices worldwide. T-Mobile and AT&T are simply getting their networks ready now, so that they can handle the demand later.

More connections equal more money
Of course, the big incentive for carriers to promote wearable adoption is the additional revenue those devices would help them generate. AT&T sells its family data plans as bundled packages, and already charges $10 a month to add network capabilities to a wearable device.

AT&T says it won't charge for its NumberSync feature, so it likely plans to make money from its per-device charge. That's a pretty good deal for the carrier, considering that once the technology is up and running, it can boost average revenue per user simply by having customers pay the additional fees to connect their wearables to the network.  

T-Mobile doesn't charge a per-line fee for additional devices right now, and may simply add the new shared phone number feature to the its long list of freebies. But that doesn't mean it won't benefit financially.

When customers connect their wearables to their cellular networks, they'll likely use more data. Right now, the average wireless customer uses about 2.5 GB of data per month, but, with the help of wearables, that number is expected to increase to 14 GB in about five years. All of that extra data usage will eventually translate into more revenue for the carriers. According to SNS Research, wearables will add an additional $71 billion in worldwide carrier revenue by 2020. 

While AT&T and T-Mobile will be the first to roll out the option of sharing one phone number between a smartphone and a wearable device, Sprint and Verizon Communications are likely close behind. But with huge wearable tech growth on the way, all the carriers should benefit. 

Chris Neiger has no position in any stocks mentioned. The Motley Fool recommends Verizon Communications. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.