About T-Mobile

You can churn cell phones using their trade in promotions, as long as you are on the right plan. And it's only worth it if you have been stacking T-Mobile discounts, and have at least 3 lines on the same plan. Families win out big here. Need to read the fine print and figure out which hoops to jump through, but it's about the same amount of effort and knowledge as churning credit card bonuses or booking hotels/flights on transferrable points.

Right now, the best plan to be on for this strategy is Go5G Plus, which is eligible for those increased trade in values.
It's $150/month for 2 paid lines + 1 free line, or 2 paid + 2 free lines if you catch the right promotion.
T-Mobile also offers BOGO lines on a regular basis, so you can get 1 paid + 1 free line for $35/month total.
Finally, you can score a permanent 20% discount on post-paid lines using an Insider Discount. Get one from a T-Mobile rep at a Costco store. If you are switching from any carrier/MVNO that isn't T-Mobile, you can also nab the big $450 Costco rebate per line ported in.

Once you are on the right plan, the steps are as follows:
1. Get a patsy phone to trade in. Buy a new or good condition used phone for ~$100, of the right model. The cheaper the better, as long as it's an eligible model. Example: new iPhone SE 3 from Straight Talk, Walmart, or a refurbished Galaxy S9 from Amazon, etc. Plenty of places. Doesn't matter if it's carrier locked, or has no phone plan, as long as it's physical condition is OK.
2. Buy your new iPhone 15, on 0%/24 month financing. Best to go directly to Apple (they have a separate carrier deals page), it comes unlocked, but from T-Mobile is perfectly fine.
3. Trade in that $100 phone you just bought and get $830 in trade-in value. You have 2-4 weeks after receiving your new phone, so plenty of lead time to get that patsy phone to trade in.
4. Sell your old phone somewhere, probably $300-$700 depending on what it is and it's condition.

You should net out about $700 + resale value of your current phone. For a big family/close friends all on the same plan, you basically get free phones every year and a small profit (yes you can do this every year, don't have to wait 24 months for financing to finish, just pay it off early and keep the bill credits).

You can do this 4 times per unique promotion. Apple and T-Mobile are unique promos, so you could've done this for 8 phones at the exact same time. Like when Go5G Plus was eligible for $1000 trade in during the iPhone 15 launch window.

This is by far the best way to get new phones on the cheap, and has been for several years now. No guarantees this will this way in the future, but it probably will still be around for 2024/2025.