To answer your original question, I think most carriers follow the same type of plans regarding new phone purhases.
They no longer carry 2 year plans from major retailers its all through device payment. I work for verizon and here is why
1) Cheaper up front cost. Instead of you paying 200$ for your device you pay the sales tax
2) Line Access goes from $40 a month on a 2 year agreement down to $20 a month on Device Payment
3) Device payment is flexible. Lets say 8 months into your payment plan you break your phone and you have no insurance. You could pay off your phone and upgrade.
4) At anytime you can upgrade, most new smart phones you are eligible to upgrade after 1 year with device trade in (allowing you to upgrade early at the sacrifice of trading in your phone)
5) No early termination fees on phones, tablets etc..
6) Does not put you into a contract.
Lets take for example if you were in a 2 year agreement and you broke your phone. Your SOL and can't do anything until that 2 years is up. If you were to try and do anything you would terminate your line and lose your number unless you bought a phone outright. Where as on DP if you have paid for the phone say 8-12 months, then half the device is paid off. Therefore you only have to shell out half the cost to upgrade your phone by paying it off instead of paying full retail.
If you really want to work the system. Make 2-3 payments on Device payment and then pay off the phone (remaining balance) you get to keep a 20$ line access discount and the price of the phone drops off the bill. That is what most customers do who like to not have payments, and like to lower their bill keeping the Line access discount offered through device payment.
Unfortunately you won't be able to lower your bill moving into latest and greatest smartphones all the time. The only thing that could help lower your bill depends on your plan and data usage. Some people I see daily are on very old nationwide plans that are overpriced. The newer Verizon plans offer Carryover data & Safety mode which will prevent data overages, and its cheaper. Some of the old More Everything plans are like 10GB for 100$ where the newer Verizon Plans you can get 12GB for 80$ (Just an example). There is 20$ you could put towards your device payment, then when the phone is paid off the bill would lower.
While there are great promo's we had Galaxy 7's and Iphones as low as 10$ a month around black friday and Christmas where a lot of customers who were already on DP (Device Payment) or formerly known as "Edge" lowered their bill. Most of the phones when they come out range from 20-27$ per month on DP. Some people were paying that, paid off their phones and upgraded to lower their DP price to 10$ a month which saved them money. Currently the Moto Z and Z force are 50% off so you could get a phone that is usually 26-30$ per month for 13-15$ and the latest and greatest motorola.
Plus if you have a work discount all the base plans are allowed to be discounted as long as your plan is over $34.99 in price.