The new iPhone 6s and 6s Plus hit stores on Friday and their sales are expected to hit a record 12 million to 13 million phones during the first weekend. At a glance, the latest iPhones have not changed mush compared to last year's models, which had been redesigned. However, the new iPhone 6s and 6s Plus boast improvements such as new cameras and 3D touch, a display technology based on a "Taptic Engine" that responds according to how hard users press their screens. In addition, according to repair firm iFixit, a teardown analysis of the new devices showed that their battery capacity is down a bit - 1715 mAh compared to the 1810 mAh battery found in last year's iPhone 6. The reduced battery size could help accommodate the Taptic Engine. Apple has said battery life is unchanged in the new phones.

At center stage there is the Apple A9 processor with 2GB of Samsung RAM. Providing connectivity is a Qualcomm MDM9635M LTE Cat 6 modem and a Qualcomm WTR3925 radio frequency transceiver.

The new iPhones use chips made by Qualcomm, Avago Technologies, Qorvo's TriQuint Semiconductor and RF Micro Devices, Toshiba , Texas Instruments and Skyworks Solutions, among others.

iFixit also said that the display of the iPhone 6s is bigger, weighing in at 60 grams, which is 15 grams heavier than the display in the iPhone 6. This extra weight is likely made up of the extra capacitive sensors needed to make the 3D touch feature work.

The iPhone 6s and 6s Plus, which start at $199 and $299 with a two-year service provider contract, go on sale on Friday in Australia, Canada, China, France, Germany, Hong Kong, Japan, New Zealand, Puerto Rico, Singapore, the United Kingdom and the United States.

For the first time ever, Apple is offering an iPhone Upgrade Program for the 6s and 6s Plus, which allows you to pay Apple monthly installments for a new phone instead of paying your carrier. Those plans start at $32.41 a month for the 16GB 6s and $36.58 a month for the 6s Plus.

AT&T is also selling the new iPhones. AT&T’s Next plans let you pay $0 down for your new phone and spread the payments over 20, 24, or 30 months, though you’ll be able to trade in your old phone after 12, 18, or 24 months and upgrade to a new version. AT&T also still offers 2-year contracts.

T-Mobile's new Jump On Demand installment plan for the 6s lets you pay $5 a month with no money down, and the 6s Plus is just $9 per month. After 18 months, you either give the phone back or pay $164 to pay it off in full. However, to get this deal, you must trade in your old iPhone 6 or iPhone 6 Plus-if you don’t have a phone to trade in, you can still sign up for the Jump On Demand upgrade plan for $20 a month.

Sprint responded to T-Mobile’s plan with its iPhone Forever program. Sprint customers can buy a 6s for as low as $1 a month and the 6s Plus for $5 a month-but only for trading in an old iPhone 6 or 6 Plus. If you have an iPhone 5s, you can still trade it in for an upgrade-$10 per month will get you a 16GB iPhone 6s, or $14 per month will get you a 16GB iPhone 6s Plus. If you don’t take the trade-in offer, the 6s is $22 a month and the 6s Plus is $26 a month.

Verizon is offering two options: Pay the full price up-front and be done with it, or spread the full price over two years. Either way, you’re paying off that phone. But Verizon is offering big bucks for old iPhone trade-ins, which could bring your costs down. Trading in an iPhone 6 Plus will get you $400, and a 6 is $350—that’s more than the $325 Apple offers for an iPhone 6 trade-in.