A new Xbox One build is available to those in the Preview Program, as well as users on Dev Mode. The build is 14389, and it offers the ability to pay for digital content by using your mobile carrier account.
Presumably, this is another method of unifying the Windows 10 platform. After all, you can pay with your mobile account on your Windows 10 phone, so you should be able to do the same on your Xbox One.
Unfortunately, the only US carrier that seems to support the feature at this time is Sprint, a carrier that doesn't even offer any Windows 10 phones. The company did offer the Lumia 635 for a time - as well as some third-party devices, such as Samsung's ATIV S NEO - but nothing that received an official upgrade. Also, due to the nature of Sprint's network, customers are unable to use unlocked phones.
Other features that we've seen in recent Preview builds include the ability to shut off 'Hey, Cortana' voice commands in favor of using the classic Xbox commands, a feature that some users have been requesting.
If you'd like to use your Sprint account to pay for digital content on your Xbox, you can do so by going to your payment options, choosing to add a payment option, and selecting the option for mobile.