iPhone 6 pre-orders begin on September 12th, with the devices set for sale on the 19th. If you’re ready to pick one up—no matter if you’re a loyal iPhone user or an Android user about to make the switch—now is the time to check your upgrade eligibility.

Luckily, as highlighted by TUAW, there are a few different ways to check—none of which require a store visit or hold-time while calling your carrier. And if you are in fact eligible, find out how to get up to $400 for your soon-to-be old device right here.

Check with These Carrier “Upgrade” Codes

The “Big 4” carriers all have special codes that you can either call or text to check your upgrade status. Just dial these codes from your Phone app, or send a text to them. Usually, you’ll get an instantaneous response, but sometimes it may take a minute or two.

• AT&T: *639#
• Sprint: 1311
• T-Mobile: #874
• Verizon: #874

You could also sign-in to your account online to check your upgrade eligibility, but that’s too much work, if you ask me. Either way, you won’t see the upgrade prices. For that, check out the next option below.

Unfortunately, AT&T customers will all get the same response back, pushing their AT&T Next program. Fret not, there are other ways…

Check on Apple’s iPhone 6 Order Page

Apple’s iPhone 6 pre-order page can do all the work for you, as well. Simply choose the model (6 or 6 Plus) and color, then hit the Check your upgrade eligibility option (T-Mobile customers can only buy the iPhone 6 at full price through Apple).

From there, you’ll need to input your phone number, and either the last four digits of your social security number, or your account’s PIN (or other identifier).

Additional Information for AT&T Subscribers

There is quite a bit of confusion with AT&T Next, so allow me to clear a few things up (thanks to mike1123 over at the MacRumors forum).

1. Currently in a contract; began before 1/19/14

If you are currently on a two-year contract that started before January 19, 2014, you can upgrade and keep your current device (or get some money back for it).

2. Currently in a contract; began on or after 1/19/14

If you began your contract on or after January 19, 2014, you will need to wait the full 20 months from the date your contract was initialized—this is the real “bummer” situation. If you’re in this boat, give AT&T a call to see if they’re willing to work with you, especially after you mention that you’re considering a switch to another carrier that will pay off your early termination fee.

3. Currently on the Next plan; payments finished

If you are already on a Next plan, things get a bit murkier. If you have made all of the payments—20 on the 12-month plan, 24 on the 18-month plan—you own your phone and can upgrade to a new one while keeping or selling your old one.

4. Currently on the Next plan; 12 or 18 payments made

If you’re on the 12-month plan and have made at least 12 payments, you can upgrade via trade-in, or pay off the remaining months and upgrade while keeping your old phone. Same deal with the 18-month plan—18 payments gets you the upgrade via trade-in, finishing the remainder of the payments allows you to keep your old phone.

5. Currently on the Next plan; less than 12 or 18 payments made

If you’ve made less than the minimum payments, you can still upgrade by paying off the difference. So, if you’re on a 12-month plan and have made 10 payments, you can pay off the remaining 2 to upgrade via trade-in, or pay off the full amount (10 payments) to upgrade while keeping your old device.

Some Example AT&T Scenarios, Because It’s Pretty Confusing

Here’s an example of some scenarios involving the 12-month, 20 payments plan:

• 20 payments: upgrade and keep old device
• 12 payments: upgrade via trade-in, or make 8 additional payments to keep your old device
• 10 payments: make 2 additional payments to upgrade via trade-in, or 10 additional payments to upgrade and keep your old device

Here’s where resale value comes into play, using a $32.50/month payment on the 12-month plan. Let’s say you’ve made 18 payments on a 20-payment plan. Sure you can upgrade now, but you’d forfeit your device and those extra 6 payments over the minimum. In this case, it would be more practical to make the remaining two payments (32.50 x 2 = $65), upgrade, and sell your phone for $400—leaving you with $335 to pocket.

But, if you’ve made the minimum of 12 payments, you’d have 8 left to own your device outright. That means you’d pay another $260 (32.50 x 8) to own your device. It may still lead to cash-in-hand, but not as much.

Whoo! Did you get all that? If not, leave me a comment below or hit us up on Facebook and Twitter—we’ll get you squared away.