system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: The new "Unlocking cell phone law."
gpt
To understand the new law, you need to understand what the law was.  So first some history.

In 1998 the U.S government passed the Digital Millennium Copyright Act (DMCA, the same thing you see if you see a takedown notice on Youtube or Google).  Included in that (in addition to the copyright provisions themselves) was a prohibition on circumventing what are called "Digital Rights Management."  In laymen's terms it's a bit like both making it illegal to take your television *and* making it illegal to break your door lock in an attempt to get your television.

The DMCA gave the librarian of Congress the power to exempt certain things from DMCA regulations.  Basically, he could say "so, yeah, rooting your iPhone *is* a circumvention, but all it's doing is letting people use their phones to their fullest capacity, so we're going to exempt it" (which actually happened).

The issue of cell phone unlocking came up, and the Librarian of Congress elected *not* to exempt it.  But did provide a window for people to unlock their existing phones without running afoul of the DMCA.  The idea was that while it made sense that anyone buying a new phone could simply buy an unlocked version, it wasn't fair to stop people who got their phones prior to the rule coming down from unlocking them.

So, about a year ago, that grace period ended and it became illegal (under the DMCA) to unlock a cell phone.  Recently, Congress passed legislation to amend the DMCA to exempt cell phone unlocking.