"Connect with - and pay for - a mobile data plan on your Windows 10 device using only your Microsoft account information. That means no fixed contract and no long term commitments to a mobile network operator. Now you can buy and use mobile data at your own convenience. This is the easiest way to get online using a trusted nationwide network. Purchase a plan via Windows Store anywhere network coverage is available."
The plans are prepaid and charged to users via their Microsoft Accounts. They are not long-term plans; they are one-time purchases for the amount of data and time specified by the plans
.The app will work with "specific" Windows 10 devices (according to the Store, only Intel-based ones) and requires a "Microsoft SIM card."
The app can be downloaded now, and includes a frequently-asked questions document that mentions that cellular data plans will be available initially in France, the UK and the U.S. According to the FAQ, the plan is valid in the country where it is purchased and does not including roaming, so it won't work in other countries beyond where it was purchased.
There's also mention in another accompanying document of Transatel, a mobile virtual network enabler and aggregator. Transatel enables non-telcos to act as MVNOs. To me, it looks like Transatel is the company providing what is designated as the required Microsoft SIM card for the new Windows 10 cellular app, as there's a "Transatel DataSIM for Microsoft Windows 10 enabled devices" mentioned in the document, which notes that the SIM card and cellular services are being provided by Transatel.
Microsoft has only a couple of models of its Surface tablets that have built-in LTE connectivity. I've heard from a number of users who wish the Pro family would include built-in LTE as an option. I guess existing Surface Pros wouldn't be able to use this, since they don't have a SIM slot, as noted by a couple of my readers. But maybe it could work for other users of non-Surface Windows 10 PCs and tablets who want this option?
The Cellular Data App in the Store isn't marked as a preview or beta. I've reached out to Microsoft to find out when it will be functional and how much the data plans will cost.
Update No. 2 (January 9): Unsurprisingly, Microsoft isn't ready or willing to clarify much at this point. A spokesperson sent the following statement:
"We are always exploring new features for Windows 10. Right now, we are exploring additional ways for customers with Windows 10 PCs and tablets to connect to data services. We have nothing further to share at this time."