Mainly because they have control over software upgrades, they do not need to update the update of a network provider every time they want to publish an update. Even if you do not buy the device directly from a particular carrier, but buy it from a retailer like Amazon or Best Buy, and it for a particular user, it probably has a carrier lock on it. Unlocked phones are also useful when traveling to areas in the country where your current carrier is not the dominant carrier. Just switch to the dominant carrier who uses the phone technology to get better reception. Iphone 5s Gold Unlocked Best Buy here. How To Make Phone Unlocked. GSM differs significantly from its predecessors as both Signaling as well as voice channels are digital reputation quality, which means it is considered a second-generation (2G) mobile phone system. Carriers did not like this because this could lead to business loss, and in 2013, The Digital Millennium Copyright Act made it illegal to unlock mobile phones.