Our recent tests of the iPhone 7 and 7 Plus confirmed they’re the best iPhones yet—and among the best smartphones you can buy. But if you're in the market to buy one, what you may not know is that some iPhone 7 models give you broader options if you ever want to switch cell-phone providers. 

Of the two versions sold in the U.S., the ones sold by Verizon and Sprint offer the most cell-provider choices.

These phones have the hardware needed to work with both GSM and CDMA networks, so those phones will work on any of the four major carriers: Verizon, Sprint (CDMA) and AT&T, T-Mobile (GSM), as well as the many smaller cell providers, such as Consumer Cellular, that piggyback on carrier networks.

The iPhone 7 models sold to AT&T and T-Mobile customers, however, are slightly stripped-down versions, at least regarding network compatibility.

They only work on GSM networks, so customers will be out of luck should they decide later to switch their carrier, using the same iPhone with Verizon or Sprint, or Credo, or NetZero, or Boost, or any of the many other carriers that use CDMA networks.

Given the equal pricing for these relatively expensive smartphones, it’s only reasonable for any iPhone 7 owner to prefer the more network-agnostic version, if only to have more trade-in options.

The network option was the only significant difference we found in our tests of the iPhone 7 and 7 Plus. In all other respects—camera image quality, battery life, etc.—they performed the same.

We should point out that Apple confirmed these details of network compatibility.

We also asked AT&T and T-Mobile if there was some reason the GSM-only phones would work better on their networks than the CDMA/GSM models. Neither company would cite a reason for consumers to prefer the more restrictive phone.

Check the top smartphone cameras in our reviews and the and see our reviews of phone plans and carriers.

Buying the Phone You Want

So how can you buy the more versatile phone if you're starting out as a T-Mobile or AT&T customer? One thing you can't do is visit the carriers' stores and ask for it. They only stock the limited cell-service models. 

Until this week, your only option was to walk into an Apple Store and pay full price. Going online wouldn't work, because Apple required you to sign up with a carrier before shipping you a phone. And the company wouldn't send you a CDMA-compatible phone if you were an AT&T or T-Mobile customer.

The in-store experience was somewhat hard to navigate, too. When we visited an Apple store a few days ago, we needed to initially ask for a Verizon or Sprint phone, and then do some negotiating once the salesperson brought it out.

Now that's changed. Customers can go online or into an Apple store and just buy an iPhone 7 or iPhone 7 Plus without a SIM card, and then take the phone to any carrier.

Do this, and you'll get the versatile model. This is a good move for AT&T and T-Mobile customers who want to retain the option of later using the same phone with another carrier.

And what if you're a Verizon or Sprint customer? In that case you can buy your phone either from Apple or from the provider. Verizon told us it automatically unlocks its phones when the terms of the agreement are met, such as at the end of a contract or when you’ve paid off your phone. And their phones aren't locked at all if you pay full price up front.

Ditto for Sprint customers, except they have to ask customer service to unlock their phone. Sprint also has the additional requirement that a phone be active on their network for 50 days before it can be unlocked.

If you already have an AT&T or T-Mobile iPhone, you probably shouldn't sweat it: Your phone works as well as any iPhone, and all this only matters for people who want to switch carriers.