Yes, of course there’s a catch.

Getting a “free” device sticks you with your phone provider for up to three years. You generally need to pay for a relatively high-priced unlimited data plan.

Taking those iPhone discounts is still a great choice for many people. But not for everyone.

I crunched the numbers from my cellphone bills and those of Geoffrey A. Fowler, The Washington Post’s personal technology columnist.

Geoff would probably save money if he took advantage of an effectively free new iPhone 15 from his wireless provider, AT&T. I’m better off shunning iPhone discounts like that.

The difference is Geoff has a typical service plan from a big three phone company. I, a weirdo, do not.

I’ll walk you through the math for the two of us. It’s a starting point if you want to do the calculations for your household.

Even if you change nothing about your phone and mobile plan, it’s worth considering the price of loyalty to your phone service.

The mobile service market in the United States is actually competitive, if you look beyond the big three wireless companies. Most people never do.

Send me your questions about the new iPhone 15 or the phone companies’ iPhone 15 discounts to shira.ovide@washpost.com. I’ll try to answer them.

Don’t make Geoff’s mistake

Geoff’s family pays for an unlimited mobile data plan from AT&T but typically buys new iPhones from Apple.

Sorry, Geoff, this is the worst choice.

He’s paying a relatively high monthly cost for phone service — about $62.50 per phone line before taxes, fees and an organizational discount but including an autopay discount. But Geoff is missing out on free(-ish) money from AT&T for a new iPhone.

(Read the “One Tiny Win” section below for details of the discounted iPhone 15 offers from AT&T, T-Mobile, Verizon and Apple. Rule of thumb: If you have an unlimited plan from the big three and are okay committing to it for a few years, the mobile providers’ iPhone discounts are better than Apple’s.)

I’m the polar opposite of Geoff. I would be worse off if I went with one of these cellphone providers’ iPhone 15 deals.

I pay full price when I buy a new phone, but my phone bill from a small wireless provider called Google Fi currently averages about $31 a month before taxes and fees. (Yes, Google sells wireless service.)

I pay only for the amount of data I use on my phone, rather than a flat bill every month as Geoff pays.

It makes sense for me because I use relatively little data — about 0.5 GB last month compared with Geoff’s 9 GB, which is fairly typical.

For me, it doesn’t make sense to switch to a pricier unlimited data plan from a big wireless company – even if I got a free new smartphone.

Over three years, let’s assume Geoff continues to pay $62.50 a month before taxes and fees for his mobile plan. He’s taking AT&T’s offer for a free iPhone 15 Pro for trading in his comparable two-year-old model.

Let’s say I buy a new iPhone 15 Pro on my own for $999 and sell an older model iPhone like Geoff’s iPhone 13 Pro to a secondhand phone company or trade it in to Apple for about $480.

Over the next three years, I estimate my costs combining a new phone and monthly phone service work out to about $46 a month before taxes and fees.

I’m not going to buy a new phone for a while, which saves me even more money.

Apple is switching iPhone cables again. This time, that’s good.

Looking beyond the big three wireless companies

These calculations show two things. First, there’s no best wireless plan or phone deal for everyone.

It’s a pain, but it’s worth comparing all your mobile plan options, especially when you’re considering buying a new phone. Consumer Reports has a guide to finding the right cellphone plan for your family.

Second, more people should consider cellphone providers other than AT&T, T-Mobile and Verizon.

Fewer than one out of every 100 customers of the big three phone companies switch their provider each month.

Partly, those free or discounted smartphones keep people from defecting. You lose a chunk of your discount if you quit before two or three years.

For many people, that lock-in is worth it.

But alternative wireless providers including Xfinity, Spectrum, Mint, Consumer Cellular, Boost Mobile and Google Fi use exactly the same mobile networks as Verizon, AT&T or T-Mobile but charge you less.

Unlimited plans can start as low as $30 a month per line or far less if you don’t use much data like me. (Wirecutter has a handy price chart here.)

Costs are lower partly because these alternative wireless companies don’t typically give you extra goodies like free streaming services included in your phone plan. They may not have in-person stores. And they might not discount new phones much, if at all.

These alternative providers aren’t the right choice for everyone, but they’re definitely worth considering.

Geoff’s family just ordered two free or nearly free new iPhone 15 Pro models from the phone company. He’s happy.

I’m happy skipping those deals and sticking with my cheaper monthly bills and the freedom to buy a new (or used) phone and switch phone providers whenever I want.

• Should you buy a new smartphone or smartwatch now or wait? Our quiz can help you decide.
• France said iPhone 12 models have dangerous levels of radiation. Basically, don’t worry about it. (Apple will update iPhone 12 software in response to France’s demands.)
• In a win for everyone, Google said it would keep updating software for Chromebook computers for up to 10 years. This means people and American schools, which use lots of Chromebooks, can use the devices for much longer instead of replacing them after a couple of years. (WSJ)

How the big phone companies’ discounts work: Typically, you need to trade in a relatively recent model of iPhone to qualify for a free or reduced cost iPhone 15 model from AT&T, T-Mobile or Verizon.

If you buy a new iPhone 15 model from Apple, the company's discounts from trading in an older iPhone aren't as generous as the phone companies'. But this gives you more flexibility.

Credits on your bill: The phone company typically credits your service bill for some portion of the monthly equivalent value of the new iPhone over 36 months (AT&T and Verizon) or 24 months (T-Mobile).

You don’t have to stick around that long. But if you quit early you typically must pay the portion of the phone for which you haven’t yet received credits. You lose some of the original discount.

This Wall Street Journal article has helpful info, too, including using Apple’s website to compare each phone company’s offers on the iPhone 15 models.

Up to $1,000 off the iPhone 15 Pro or Pro Max models. Up to $830 off the iPhone 15 or 15 Plus.

If you have an eligible iPhone to trade in: The maximum discount on the iPhone 15 Pro and Pro Max may only apply if you trade in an iPhone 12 Pro Max or any iPhone 13 or iPhone 14 model. Models older than that have a lower trade-in value.

If you're buying an iPhone 15 or 15 Plus, the maximum discount applies if you trade in an iPhone 11 or newer.

And if your service plan is: one of the “Unlimited Your Way” plans.

AT&T has an offer to pay $15 to $20 a month over 36 months for a year-old iPhone 14 model. That’s a hefty saving off the list price. You don’t have to trade in an older phone but you need an eligible unlimited service plan.

Up to $1,000 off any iPhone 15.

If you have an eligible phone to trade in: The maximum discount may only apply if you trade in a Pro or Pro Max iPhone 11 or newer. Other iPhone models have a lower trade-in value.

You can trade in some Android phones, too, directly with T-Mobile.

And if your service plan is: select Go5G phone plans. There are smaller device discounts available if you have other T-Mobile plans.

Up to $830 off on iPhone 15 models for existing customers.

If you have an eligible phone to trade in: Verizon suggested people check on trade-in deals on its website starting today. It looked to me that maximum trade-in values applied to the five-year-old iPhone XS and newer models.

And if your service plan is: some unlimited or 5G plans for existing customers.

If you’re a new customer or adding a line, it’s up to $1,000 off an iPhone 15 model if you trade in any iPhone and have a higher-tier unlimited service plan.

Up to $650 off an iPhone 15 model.

If you have an eligible phone to trade in: Apple offers trade-in value for iPhone 7 models (up to $40) to last year’s iPhone 14 Pro Max (up to $650).

None of this should persuade you to buy a new iPhone that you don’t need.

The absolute best choice for your wallet and our planet is buying less new stuff. It’s better to keep your existing phone as long as you can, repair or replace parts as needed and buy a used phone from a reliable seller.