Apple's new iPhone 6s and iPhone 6s Plus are approaching their release date, which is Sept. 25, 2015 around the world. Here's what you need to know to get the best deal on a new iPhone 6s or iPhone 6s Plus this Friday.

Apple iPhones have always been a top seller, demanding premium prices that used to be mitigated by the wireless carriers' subsidies. It's why you could get a brand new iPhone upon its release date in the U.S., valued around $700 for only $200 or so. The only string attached was a two-year contract.

Now, as the wireless industry shifts away from subsidies and towards monthly installments and being open to customers buying smartphones themselves -- unlocked, at full price -- and joining their networks, the total selling price of the new Apple iPhone 6s and iPhone 6s becomes a lot more important.

In the U.S., the bare minimum you will pay for an unlocked Apple iPhone 6s is $650, and that's for the 16GB storage level, which doesn't get you far these days.

More storage costs more, with the 64GB version of the iPhone 6s costing $750 unlocked, and the 128GB unlocked iPhone 6s fetching $850. Yikes!

So carriers, and Apple itself, are trying to make the change more palatable with payment plans, trade-in deals, and special offers.

For example, Verizon Wireless offers the iPhone 6s starting at $27.08 per month with zero down when you sign up for the 24 monthly payments, which of course means you're still on the hook for two years.

The iPhone 6s Plus on the same payment plan starts at $31.24 per month for 24 months. But don't forget that you still have to pay for your wireless plan on top of those payments.

Verizon is hoping to entice customers with up to $300 in gift card money for trading in certain smartphones that are in good working condition. If you switch to Verizon from somewhere else, you'll get an additional $100 credited to your first few monthly bills.

Apple is offering its own pricing plan in the U.S., starting at a less-palatable $32 per month for two years. For the iPhone 6s Plus, the same plan starts at $36.58 per month.

But as a bonus deal for early adopters, Apple's plan gives you the option to upgrade to the new iPhone every year, as you continually renew your payment plan. Say hello to the iPhone 7!

The best deal on the new Apple iPhone 6s and iPhone 6s Plus so far -- and by far -- was announced this week by T-Mobile. The wireless carrier is disrupting its own payment plan with deep discounts and additional trade-in offers through its "Jump on Demand" option, which is an 18-month plan.

T-Mobile was already currently the only place to get a discount on a new iPhone 6s or iPhone 6s Plus: It was offering the iPhone 6s starting at $20 per month with zero down upfront.

Then on Wednesday, T-Mobile announced an additional trade-in deal for a range of iPhones, Samsung Galaxy S and Note models, and a smattering of other smartphones. Depending on the trade-in, the monthly installments can get very cheap.

In fact, if you have an Apple iPhone 6 or iPhone 6 Plus from last year, or want to get rid of your Samsung Galaxy S6 already, you could end up paying $5 per month for a new iPhone 6s. If you buy out the iPhone at the end of the 18 monthly payments, the discount totals more than $100 off the list price.

To check out all the different options through T-Mobile, check out an exhaustive chart of pretty much every permutation of trade-in deals, put together by Redditor 50atomic (via BGR).

There's still some time left before the new Apple iPhone 6s and iPhone 6s Plus hit their release dates, so stay tuned to see if other sales, discounts, or trade-in offers are announced by other retailers and carriers.