If I walk into an Apple store and can show that this serial number appears under "my devices," can they and will they unlock for me so we can set it up, fresh?

It refers to the Activation Lock feature, which is part of Apple’s Find My iPhone service, which is designed to prevent unauthorized use of an iPhone if it is ever lost or stolen.

The Activation Lock on an iPhone is a feature designed by Apple as a security measure. It is part of the Find My iPhone service, preventing others from using your iPhone, iPad, iPod touch, or ...

Some iPhone thieves are exploiting a security setting, called the recovery key, that makes it nearly impossible for owners to access their photos, messages, data and more.