So let me get this straight
If I choose to purchase let's say... a T-Mobile-branded phone from eBay. The seller on eBay states the phone can be activated without contract. The phone may or may not ship with original software from T-Mobile. I receive said phone and install a SIM from a T-Mobile MVNO like Simple Mobile and it works fine. I'm still breaking the law anyway?
Some of these phones are rooted and flashed with custom ROMs that work much better, but that's now illegal as of Sunday?
How can this be remotely enforceable anyway? They're now going to access everyone's phones OTA and take a peek at the software version and build?
No, this issue really only applies to a small target. iphones, particularly on Sprint, and some on Verizon. They are locked so that they cannot be used on ATT and T-mobile even though they have sim card slots and have the ability to work. The exemption would allow a user to circumvent the lock and use their phone on a domestic network. That is expiring tomorrow.
Virtually every other phone can already be unlocked legally by the carrier/manufacturer, often well before a contract expires.
In my opinion you either don't do business with carriers that refuse to unlock your device, or you choose devices the carriers will unlock (if any).
Sprint and Verizon refuse to allow phones from each others network to be activated. ATT will take devices from other networks but will force you into a plan they deem appropriate for your device (usually mandating a data plan). T-mobile is the lone star here that allows you to bring any device and use it with any plan (including non data plans) and they don't have any devices they will not unlock upon request.