This isn't DRM
What is the exact "digital right" they are managing by locking to a carrier? Unlocking isn't about copying or copyright at all and the phone itself isn't the property of the carrier nor is the operating system (eg iOS, Android).
I usually buy unlocked to begin with, but my kid lives in the EU. She can use any unlocked GSM so I can give her my old ones.
I unlock and root just to get rid of carrier crap, entertainment of all types, social media of all types. No DRM involved, dammit.
There are quite a few weather apps, astronomy apps, nature apps that simply don't run on a dumb phone.
Some movie named Inception or something like it was included on some TMO phones. I guess it was on the SD card - but I formatted my card first and wouldn't know. But some were looking for it. That would involve DRM, I suppose. So would music if the app is installed by the carrier.