Microsoft has already published this cellular data app to its Windows Store. Unfortunately, there is still no news on what Microsoft has in store for the service. So far, all we know about the app is that it's designed to work on Windows 10 devices and that it needs a Microsoft SIM card in order to work. The company has not disclosed information on which markets they plan to launch the SIM card in as well as how much the cellular data price will be. But they do plan to sell plans through their Windows Store so it's likely the data will be associated with a Microsoft Account.
It could be possible that Microsoft will create mobile virtual networks of its own so Windows 10 users may connect with other carriers. Since there contracts aren't necessary, it's likely that this is something Microsoft could do. Or it could follow Apple's approach in offering access through its own SIM card. That's all we know about the cellular data for now. Perhaps the company is working on providing a more detailed announcement on what this cellular data app will be. Until then, we'll have to be patient.