which iphone 6s do I need to buy for virgin mobile usa?

No. You need to buy a phone sold by Virgin Mobile specifically for use on their network.

That is not a "law". It is a voluntary agreement among the 4 major carriers in the US. AT&T, Verizon, Sprint, and T-Mobile. It places no requirements on any of the smaller carriers or MVNOs. The agreement does not affect Virgin Mobile.

You also seem to misunderstand what the agreement is. It does NOT mean that all phones are unlocked. Not even remotely. It merely defines the circumstances under which the major US carriers will unlock phones.

Virgin Mobile in the US is a CDMA carrier. They will not activate any phone that was not sold specifically for use on their network.

If you are referring to Virgin Mobile in a different country, then you need to make that clear. Virgin Mobile in most countries is a GSM carrier.

Although I subscribe to Virgin this lockout by Virginmobile from buying only phones through them cripples their customers because the phones are only intermittently available if ever. They have zero supply. Furthermore the iphone they sell is only 16gb.

I've been a Virgin Mobile iPhone customer going on 3 years, and just tonight I received my new iPhone 6s in the mail from Virgin. The model number is an A1688.

I, too, am wondering if the phone comes, somehow, "pre-locked" (for lack of a better term) to Virgin, or, if I never call Virgin to activate it, would it work with any carrier operating the LTE bands it supports. If it does, what stops anyone from buying this phone from Virgin and using it with another carrier of their choice, as it's a full $100 cheaper than anywhere else?

I note that the Apple specs do list the A1688 as being limited to LTE, but I don't really know what that means.

-- Model A1633*

LTE (Bands 1, 2, 3, 4, 5, 7, 8, 12, 13, 17, 18, 19, 20, 25, 26, 27, 28, 29, 30)

-- Model A1634*

TD-LTE (Bands 38, 39, 40, 41)

TD-SCDMA 1900 (F), 2000 (A)

UMTS/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz)

CDMA EV-DO Rev. A (800, 1700/2100, 1900, 2100 MHz)

GSM/EDGE (850, 900, 1800, 1900 MHz)

-- Model A1688*

LTE (Bands 1, 2, 3, 4, 5, 7, 8, 12, 13, 17, 18, 19, 20, 25, 26, 27, 28, 29)

-- Model A1687*

TD-LTE (Bands 38, 39, 40, 41)

TD-SCDMA 1900 (F), 2000 (A)

CDMA EV-DO Rev. A (800, 1700/2100, 1900, 2100 MHz)

UMTS/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz)

GSM/EDGE (850, 900, 1800, 1900 MHz)

If the carrier is selling the device, and it is at a price lower than the full price by Apple, you can bet the device is locked to Virgin. When a carrier subsidizes a device, then the phone is locked to their network. As a matter of fact, any phone sold by a carrier is locked to that carrier, until they authorize unlocking it.

I hear what you're saying, but don't all other carriers with the exception of Virgin require a contract in order to purchase an iPhone? My understanding is that one cannot simply order an iPhone from Tmobile or AT&T without first agreeing to a contract. I'm also unaware of any other pre-paid carrier that carries the iPhone, but I'm probably just clueless.

There are plenty of carriers out there that carry the iPhone, including many MVNOs. Many of the carriers now are getting away from contracts, but do require service, there is a difference. You can establish an account with a carrier without a contract, but generally a subsidized phone requires a contract. I'm not a Virgin Mobile customer, so I cannot speak of their requirements. Either way, whether it is contract or not, the carriers sell locked phones. The only exception is paying full-price for a phone and requesting an unlock up front.

That this question does not have a aimple answer is ridiculous. Did it take this long for some uniformity to arrive the railroads ? I want a bigger 64 gb iPhone. Virgin dies not sell that model. It is incredibltly difficult to even get a 16gb model. When I last spoke to a script reader there or are they cryptic readers said all they need is the three import numbers to activate an unlocked phone. Nothing was said about wether I will have full service with my also three year old number through them. Also I can go from one apple store to another and get different answers. What the store comes down with is that if it does not work you have 14 days to return. So the consumer gets stuck with undoing and redo all kinds of financing and activation and inactivation stuff in these very murkey and tumultous waters. When f=did you you get your 16gb iphone ?