They unlock it, but not totally. As others mentioned, it's like a partial unlock. I'm not sure to what extent, but I don't know whether I could use it on Page Plus which uses Verizon's 3G network. If it's truly unlocked, I should be able to use my iPhone 4S on AT&T, Verizon, Sprint or any network using the same technology and frequencies.
Okay, let's back the trolly up for a second and get some terminology straightened out. You are right that not all unlocks are full unlocks, but I think you're getting confused by a number of things. You can get the so-called "partial unlock" now before the end of your contract, and
typically the unlock you get once you have fulfilled your contract
is the "full" unlock, but even that depends on a few different factors. Not all carriers are equal, and what constitutes an "unlock" for you is dependent on which carrier you're on.
So one of the things that I think is confusing people here is that there is a difference in how "carrier locks" are implemented and enforced on the different kind of phones made for different kinds of phone networks. As many of you know, there are so-called "CDMA" networks, and "GSM" networks. Although there are many technical differences between the two standards (as well as many branching standards that these two have fathered), the main difference from the users' point of view is how phones on each kind of network are provisioned: GSM phones use a SIM card, CDMA phones do not. In the U.S., out of the national carriers, Verizon and Sprint are running CDMA networks, and T-Mobile and AT&T are running GSM networks.
For GSM phones, then, locking is pretty simple to understand: a SIM card has a unique serial number -- the ICCID -- that is tied to your account on the carrier's side, and the first few digits of the ICCID (the Issuer Identification Number, or IIN) identify the issuing carrier. A "SIM lock" means that you cannot put in a SIM card for any carrier other than the one that matches a given IIN, which would normally be the one that issued the phone to you. When that phone is unlocked, you can use
any SIM card in the phone. Before the iPhone, SIM unlocks were 8-digit codes that the carrier you bought your phone from knew how to issue for your particular phone, using a secret algorithm that is based on the phone's serial number (IMEI). With the iPhone, the carrier tells Apple to unlock the phone, and then Apple, authorized by the carrier, pushes the unlock to you across the internet via iTunes the next time you sync your phone.
For CDMA phones, it's a much different game. A GSM SIM card contains information that the phone needs to know about the carrier you subscribe to in order to connect to it: your phone number, how to identify its towers, and so forth. So the phone just reads that information straight off the card; simple. Since a CDMA phone doesn't have a SIM, you have to tell the phone that information by some other means. Before the iPhone, that information was actually entered manually into the phone via its keypad! There would typically be a hidden menu somewhere that you'd have to know the magic incantation to access, and even then there would be a 6-digit security code required to make any changes to the configuration. There were two kinds of codes: the SPC (system programming code), and the MSL (master subsidy lock). An SPC is a one-time-use-only code: the kind of thing that a cellular provider would feel safe giving out to a customer, say, if they were going to allow the customer the option to activate their new phone at home. But once used, it can never be used again to re-program the phone, whereas the MSL is the "master" key: if you knew it, you could reprogram your phone to use a different service provider at any time. Thus, your CDMA phone was effectively "locked" if the MSL to your particular phone was withheld from you by the carrier. With the iPhone, of course, Apple took a different tactic: there is no hidden menu in CDMA iOS phones where you can enter in an MSL and be allowed to re-program your phone number, carrier SID, and so forth. Instead, ALL of that provisioning information is sent to the phone by the carrier via iTunes (or iCloud if you elect not to sync to a computer)!
Back in the day, Verizon was actually the more liberal of the two CDMA carriers: Sprint always sold phones with unique MSL codes that they refused to give out to the end-user most of the time (though sometimes people managed to squeeze them out of Sprint with clever social engineering tricks), whereas Verizon was like, "meh, who cares," and had a standard policy of setting all of their phones to MSL code 000000, and didn't even bother to make a secret of it. So, for all intents and purposes, Verizon phones were all sold "unlocked." As far as I know, this is still their standard policy as far as feature phones go.
However, because this CDMA activation procedure for the iPhone is essentially an undocumented "black box" and is something that only the carrier who sold the phone is given access to, iPhones sold on either Verizon or Sprint are essentially "locked for life." Apple has not given providers a means to "pass off" a CDMA iPhone from one provider to another, and there is no method that anybody has discovered yet (or at least that I've heard of) to reprogram the CDMA carrier settings of your Verizon iPhone so that it tries to register to Sprint's network instead, or vice-versa; this is all handled behind-the-scenes using Apple's provisioning servers. So even though it is theoretically possible to make a Verizon iPhone talk to Sprint or the other way around (the hardware is exactly the same), there is no interface provided on the phone to do so. (And this only scratches the surface, because there is also the issue of whether certain carriers will only allow phones that they sold to be used on their network, so even if you DID have a way of reprogramming the phone, it would likely be blocked by the carrier you want to move to...yes, it is dumb; no, it does not make sense; and yes, they are blockheads that need to have a clue-bat taken to their execs.)
Furthermore, the iPhone 4S is itself a special case. It is truly a dual-network device, containing both a GSM radio and a CDMA radio. This makes things even
more confusing, because there are essentially
two carrier locks involved on a 4S: the one on the CDMA side, and the one on the GSM side. And, yes, they apparently can be controlled independently. The 4S sold on a CDMA carrier like Verizon or Sprint is "locked for life" on the CDMA side of the phone, just like the CDMA iPhone 4 is and for all the same reasons. But the GSM side can be unlocked even while the CDMA side remains exclusive to the original issuing carrier. And as both Verizon and Sprint have demonstrated, the SIM lock on the GSM side of the phone can be either partially unlocked, or fully unlocked! It seems to be standard practice for both Verizon and Sprint to give certain customers a partial unlock on the GSM side of the phone under certain conditions, even when they are still under contract. The partial unlock will allow the phone to be used with any SIM
except for ones that have an IIN that Verizon or Sprint have decided to explicitly blacklist. And both providers have both chosen to blacklist the IINs of any GSM carriers in the U.S., so the only good that such an unlock does is to give you the ability to use international SIMs in your iPhone while traveling abroad.
And finally, different carriers have different policies for when they will unlock your device and how extensive that unlock is. AT&T, for example, will not even give you a partial unlock while you are under contract for when you travel overseas, like Verizon and Sprint do, thus forcing you to "roam" on international GSM carriers and incur huge fees for doing so. But after you have fulfilled your contract, they will absolutely unlock the GSM side of your phone completely. On the other hand, Verizon and Sprint, to my knowledge, will never issue a full unlock for the GSM side of the phone, and because of the way that Apple engineered the CDMA provisioning on the iPhone, neither Verizon or Sprint can unlock the CDMA half of the phone for you
even if they wanted to, since they have not been given the power to do so by Apple.
So your question on how to escape locking in the U.S. cannot be answered without you answering the question, what do you mean by "lock"? What carrier are you on? What model of phone did you get, 4 or 4S? What carrier do you want to go to, and are you trying to stay within the same carrier "technology family" (CDMA to CDMA, GSM to GSM) or switch (CDMA to GSM or vice-versa)? If you have a GSM phone and want to move to a GSM carrier, this is the simplest to understand and to accomplish. Heck, you can even walk into an Apple store
today, pay full-price for an iPhone, and walk out with a completely unlocked GSM phone. Use it with whatever GSM carrier you wish. If you are using a CDMA provider right now, though, that's where things get complicated. In theory, you could move to a GSM provider if you could somehow sweet-talk your CDMA provider into completely unlocking the GSM side of the phone. But unless Apple changes their provisioning method for CDMA, or some clever person figures out a backdoor method for doing so, you will never be able to move from one CDMA carrier to another, nor will you be able to activate a 4S that was originally activated on a GSM network on a CDMA network. Again, not because of technical reasons, but because of artificial limitations.
The moral of the story is to boycott CDMA providers and always buy unlocked GSM phones if you want ultimate freedom.
-- Nathan
