What Does Locked Down Device (LDD) Mean?
A locked down device (LDD) is a device that can only be used with a particular SIM card. Making the device incompatible with other manufacturer's technologies is referred to in the industry as locking down the device. Many mobile devices attached to 3G and 4G wireless networks come locked down so that it is hard for buyers to switch telecom carriers.
Techopedia Explains Locked Down Device (LDD)
Locking down devices is protected by legislation that declares engineering to unlock devices illegal. Unlocking a device is a particular kind of product hack differing from the practice of jailbreaking which involves other reverse engineering or alterations for compatibility.
Jail breaking allows users to add applications or change the custom layout of factory direct interfaces. These types of modifications can void the warranty on a device, and because of specific engineering, many alterations could completely disable the device.
Although unlocking devices may be less complicated than jailbreaking, these changes can introduce security risks, for example, on Android devices where users can unlock something called the boot loader to introduce their own ROM. There are also the legal implications to unlocking devices. Some reports show that unlocking cell phones for profit could result in up to five years in prison and $500,000 in fines. In addition, in some cases, unlocking inherently requires jailbreaking to add the kinds of non-factory specific interfaces that users need to access other carriers.
Generally, there are powerful incentives for users to stick with factory provided systems and avoid altering their devices in any way.