The short story: If you want to upgrade to iPhone 5s and keep your AT&T unlimited data plan, you should upgrade through AT&T, not Apple.

After an Apple sales representative told us there was no way to upgrade to the iPhone 5s through Apple and keep an unlimited data plan, we followed up on his suggestion to try ordering through AT&T instead.

We’re happy to report that, yes, it is possible to upgrade to the iPhone 5s and keep your unlimited data plan, assuming you’ve been able to keep it alive for this long. As with the last time a new iPhone came out, you have to do it the right way or risk losing unlimited data.

If you’re eligible for an upgrade on AT&T, you can log in to My AT&T. You will then see a number of scary warnings on your way to upgrading, which seem to indicate that you might lose your unlimited data plan:

“A Data Add-on Plan is required and will be chosen for you, if applicable,” reads the bottom of the text in a pop-up window. “You may change your data plan at myAT&T. In some cases, it’s possible that some features may be removed. After you place this order, you can review your features and make updates to your account within myAT&T at any time.”

That looked like exactly what we feared, but the AT&T service representative reassured is that it would be okay:

Eliot: I don’t want to click Continue, because that means I agree to lose it. I think.

[ATT rep]: No it won’t

[ATT rep]: When you add the phone it will take you to services, There you will select the same data plan you have now only it will have a new name.

[ATT rep]: You will select the Unlimited 4G LTE plan.

Eliot: Is it still $30/month, or is it more?

Eliot: Sorry about all these annoying questions, I just want to be sure I am making the right decision. Have been hanging onto unlimited data since the iPhone 1.

[ATT rep]: The same price. It is a name change only. That is the because the new iPhone is 4G LTE

We had another, less urgent concern, due to this plan’s name (“Unlimited 4G LTE”). Would the new plan still offer unlimited data in areas where there’s only 3G coverage, or would AT&T cap our plan in those areas? The AT&T representative assured us that the “unlimited” part of the plan would apply to both 3G and LTE:

Eliot: Do you specifically mean that the unlimited data will work on 3G?

[ATT rep]: If you are in a 3G area yes.

And with that, we took the plunge, our AT&T unlimited data plan apparently intact, even though AT&T regrets ever making such a plan possible.

The verdict: If you want to keep unlimited data as you upgrade to the iPhone 5s, do it through AT&T (or your other provider), not through Apple.