An unlocked phone is a device that isn’t tied to one specific carrier. Typically, when you’re locked into a ball-and-chain monthly contract, the associated phone remains locked to that specific carrier’s network.
Why? Because wireless carriers sell phones at a discount. To recover financial losses from subsidizing, carriers lock customers into a multi-year contract while locking the phone to its network. This prevents customers from getting a discounted phone and jumping networks without paying their bill. It also prevents the sale of phones prior to paying them off.
That said, you can’t install SIM cards from competing networks and expect instant connectivity. Even if the phone has the hardware to support other networks and you’ve made all the payments, it usually remains carrier-locked until you make a formal request and meet specific conditions.
For instance, if you get the Samsung Galaxy S9 through AT&T, it remains tied to that network until you submit an unlock request. However, you can only submit this request if the device is paid off in full, you’ve completed your contract agreement, you’ve used the device for a specific number of days on the network, and so on.
Here are links to the unlock requirements for the four major carriers in North America:
Of the four, Verizon is the only carrier that doesn’t lock phones even if contracts and payment plans aren’t complete. This stems from an agreement Verizon made with the Federal Communications Commission (FCC) when it acquired block C spectrum. Verizon’s unlock stance may eventually change, as the company seeks the FCC’s approval on a new policy that will lock devices for 60 days after purchase.
In addition to postpaid plans and phones, restrictions also apply to prepaid plans and associated devices purchased through wireless carriers. These phones do not have payment plans, but carriers still want time and financial investments before unlocking these devices. For example, T-Mobile requires an active account and one of two options: Use the device for a year on T-Mobile’s network or spend at least $100 in refills.