It looks like Microsoft is planning to become a mobile provider, although Microsoft still hasn't announced any official plans for the upcoming service.
Through the Cellular Data app, Windows 10 devices will be able to get internet access without Wi-Fi, using existing mobile network operators. Microsoft will serve as an intermediary taking care of the billing, which makes the Company basically a mobile network reseller
From the App description:
“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 Cellular data app can get you connected any time with a secure, high-speed mobile connection.”
Prepaid data plans will end when users have used the purchased amount of data or by expiration. “Service is available in some markets and offers are for domestic plans only – international roaming offers will be available soon,” the listing from the app clarifies.
Pricing of the cellular data plans and when the SIM card will be officially launched are still unknown.
The Cellular Data app is featured to also work on Windows 10 PCs, which will make SIM enabled Windows 10 hybrids more attractive. In the past Microsoft offered 3G enabled Surface Tablets running on Windows RT.
However, the current Surface Pro 4 product-line is missing such mobile features. The new app might be a hint that Microsoft is also working into that direction.