regardless of whether it's subscription or you buy it outright, get it free or steal it or whatever, the T&C's of most modern tech products that have an ability to upgrade the software/firmware will give the creators the right to amend products if you agree to install it and/or update it
back in the 80s and before then you may have bought a product and it couldn't be upgraded without buying physical parts, but now people regularly buy products than can be upgraded by connecting online, and the T&C's allow the creators to make changes. usually however the consumer can opt out of upgrading and keep the item the same as it was when they first bought it, so you could install windows from the cd/dvd and just never update it. in the current world, few people are going to want to buy a new tech product and never ever updated it. most people want the latest upgrades, whether it's good bad or indifferent to them, and unless it's a hassle or they don't know how to do it, they will usually upgrade as long as they don't need to pay more money for it
looking at the bigger picture of the market, i can't see MS surviving indefinitely in the OS market anywhere near as successfully as they do if they move to a fully subscribed market. they may offer a particular version that is, but as the majority of users will be regular home consumers rather than businesses, i can't see many people going for this, especially in poorer countries. it's certainly not something that's going to happen in the short term, and it definitely isn't the norm at the moment. they aren't going to stop any current versions of consumer windows from working unless people pay a sub
regarding phone contracts, in the uk at least you typically just get one contract and one price for both phone and airtime/service
btw