But what about phones that you pay outright full price for? Shouldn't they be unlocked? Absolutely. Are they? Not in all cases. Today, each carrier has its own policy on unlocking phones sold for use on their respective network. With the industry now moving away from subsidized phones to phones that are purchased on installments, contracts are becoming less prevalent. But with phones on installment plans, the carrier still locks those phones to their network to insure the device is paid in full. Most carriers will now gladly unlock any iPhone purchased and paid for in full with a fulfilled contract without hassle or delay. The exception to this is Sprint. They claim only phones sold after February 11, 2015 can be fully unlocked. Devices sold prior to this date can only be unlocked for international use. While most carriers implemented all six provisions of the CTIA agreement for unlocking over six months ago, Sprint is the only one who refused to implement them till the last minute--and did so with caveats. (The industry decided to adapt the CTIA provisions to avoid having the FCC write rules that forced them to unlock--that action was imminent had they not voluntarily offered to provide consumer relief).
While Verizon and Sprint both use CDMA technology where most world carriers including AT&T and T-Mobile use GSM, Verizon and Sprint phones are not always if not ever interchangeable. In other words, a Sprint phone may not be usable on Verizon, or vice-versa. Yet both Sprint and Verizon phones should be compatible with AT&T and T-Mobile, although not 100% with data given the different frequencies and bands used. Most AT&T or T-Mobile GSM phones are interchangeable on each others networks, but neither AT&T nor T-Mobile phones are compatible with Sprint or Verizon since they don't have CDMA radios needed to access those networks. Yet Sprint and Verizon phones had to add GSM radios to their devices so subscribers can take their smartphone overseas and be able to access international carriers or insert a foreign carrier sim that is compatible with the GSM carriers worldwide.
AT&T will allow you request an unlock online if your device is off contract, account is paid in full if closed, and you don't owe a balance on some installment plan. Your request is supposed to be fulfilled within 48 hours if all stipulations and obligations are met.
T-Mobile locks their handsets and will also allow you to request an unlock by calling them. Within 48 hours, they will email you the unlock code and instruction on how to unlock. Again, you must be contract-free, not owe any EIP (Equipment Installment Plan) and the device must not have been reported lost or stolen, and the account it was attached to must be paid in full. Requesting an unlock from T-Mobile is also straight-forward without hassle once all the requirements are met.
Lastly, Sprint has finally fallen into the fold after insisting on waiting till the last moment, while the other carriers complied with all of the CTIA provisions almost immediately. Sprint today says that all devices sold after February 11, 2015 can be fully unlocked. However any device sold before that date can only be unlocked for international use. This shortcoming flies in the face of the whole spirit of the CTIA rules and pretty much tells former Sprint customers to go pound sand. It's no wonder Sprint keeps bleeding subscribers (not to mention having the worst network and abysmal customer service).
Sprint says that it too will unlock devices when they are contract free, have no account balance due, and are not under a finance contract. It's not clear if you still must have a current active Sprint account to get an unlock, which was also a requirement to get an international unlock before the CTIA rules became fully effective. If this rule is still in effect, this means you should request your unlock BEFORE you quit Sprint. No other carrier has this requirement. Again, a pain no one should have to endure.
So why would you want to get your device unlocked, and why should you care? Many reasons. First of all, so you can take your device across the street to another carrier if you so choose. Or if you travel overseas and want to use an international sim from a local carrier, you'll want your device to be unlocked. And the most important reason is that it adds value. A carrier unlocked device will fetch more money than a locked model of the same if you decide to sell it to buy a new model--anywhere from $15-$100 more depending on the device.
Cell phone unlocking is a long time coming, and now that unlocking is no longer illegal (it was for a couple of years), it makes sense that your fully paid-for device shouldn't be tethered to one carrier. Ask for an unlock as soon as your device is eligible--why wait till you need it? It makes sense to be ready for any upgrade or travel without having to worry if your device will work when you need it to with an alternate carrier. The device is yours, just make sure you're not beholden to any carrier Kids!