The following is an updated version of a post I made to Google+ regarding the Cellphone/Tablet Unlocking/Jailbreaking law that went into effect in the US 29 Jan 2013.
 
10 things you need to know about the Unlocking/Jailbreaking law that goes into effect at midnight.
 
(I am not a lawyer.  The suggestions below are consumer advocacy suggestions, and not legal advice.  I have made all of the suggestions below previously, and independently of any law.  Comments on US law are my personal opinions only.)
 
1.   My understanding is that the law is not retroactive to devices purchased prior to 29 January 2013.  It also does not apply to used devices or "legacy phones"  (what is meant by this is not clear in the law, but it seems to allow unlocking of discontinued models.)  It also does not apply to cases where a wireless provider gives you an unlock code, or grants you permission to obtain an unlock code.
 
2   The simplest and most obvious way to avoid any question of legality, (and what I have said all along) is to NEVER buy a provider-locked device.  It is never in your best (long-term) interest, and now it could cause you to run afoul of the law at some time in the future.
 
3.  Buy from US vendors that sell unlocked (and sometimes rooted) devices.  Most Google Nexus devices were sold unlocked.  My Google ADP-1 (Android Developers Phone) was purchased factory unlocked and rooted directly from Google.
 
4.  Buy from overseas vendors.  Most Chinese phones are sold unlock, and if you know what you are buying, they can be very good phones. Not all Chinese phones are "fakes". Vendors in the Orient, and in Europe sell perfectly legal, real, unlocked phones all the time.  In some countries (such as Israel), it is illegal to sell a locked phone. (Now why our government would pass a law that sends business overseas, I have no idea.)
 
5.  Keep receipts.  Ask vendors to indicate Make and Model, and locked/unlocked status on the invoice or receipt. This helps ensure that you get what you think you are getting.
 
6.  For most devices, regardless of screen size, you can install VoIP software, and register with a service that allows you to make calls to real phone numbers.  It is then unquestionably (assuming common sense still exists,) a phone.
 
7.  (Android) Rooting is not always necessary to do what you need to do.  Some devices (even if they do not allow root from the device) have ADB (the adbd daemon) running as root.  On such a device you can do customization, filesystem repair, data recovery, etc. without permanently rooting.
 
8.  Prepare for a little teasing from your overseas friends who don't understand US law. They are not going to understand why we can own an assault rifle, but not a mobile phone. -- Think about it --  You cannot OWN the cell phone.  Locking allows the wireless carrier to retain control, and thus "ownership" of the phone.  After midnight, truly owning a new cell phone will be illegal in the US (unless you can prove it was never SIM locked in the first place, or purchased prior to 29 Jan 2013).
 
9.  Keep your nose clean.  Unlocking, Rooting and Jailbreaking have legitimate uses.  I have unlocked, rooted and Jailbroken many devices, but I do not endorse or facilitate piracy or theft of intellectual property. I support the classical interpretation of ownership of property and the right to do what I want to devices I have legitimately purchased.  ("to" is different than "with", and that is why this law is radically different than any other law I know of)
 
10.  Have faith in the US justice system.  It may take a while, but the nonsensicallity of parts of the DMCA will become obvious.  The wheels of bureaucracy have to turn, and the lawyers on both sides have to get a little richer, but the DMCA has been changed, revised, corrected, and amended in the past and it will continue to do so.