Today, Sprint got tired of trying to win over customers from bigger wireless players like AT&T and Verizon, and decided to take a swing at T-Mobile, offering up to $350 for T-Mo subscribers willing to switch and trade in their phones. But there’s something off about the math Sprint is using to compare its plans to T-Mobile’s.

In making the case for customers to jump ship from T-Mobile, Sprint uses the following comparison of monthly costs for having a Samsung Galaxy S5 on the two providers:

Seems pretty straightforward, until you ask why the installment price for the phone is so different ($20/month for Sprint; $27/month for T-Mobile).

Then you notice that the Sprint price is actually for leasing the phone for 24 months. That means at the end of that two years, you have to either trade-in your leased phone and start leasing another device or pay off the remaining balance for the original full price of the phone. That means you’d be on the hook for $170 if you want to keep your phone.

So you either get stuck in a leasing carousel and can never enjoy the financial benefit of not having to make monthly payments on your phone — even if it’s only a few months — or you end up paying the same as you would via T-Mobile, except you’re slammed with paying a lump sum of $170 to hold on to a 2-year-old phone.

This is why Sprint doesn’t use it’s own Easy Pay installment numbers for the comparison in this chart, as those monthly payments come out to — you guessed it — $27/month for the Galaxy S5.

Which is odd, because you’d think the $20/month difference between the two providers’ unlimited data plans would be sufficient reason for customers to consider switching.

However, recent tests have shown that Sprint’s current LTE speeds are woefully behind the competition, while T-Mobile’s are now competitive — and in some cases faster — than AT&T and Verizon. So while you might, in theory, have access to unlimited Sprint data, you might not be able to actually enjoy all those gigabytes of data.

Meanwhile, for the same $60/month as the Sprint unlimited plan, T-Mobile offers 3GB of data. Since many people don’t use that much per month, 3GB may suffice. Additionally, T-Mo recently began rolling over unused data in “Data Stashes” that remain available for use for 12 months.

We’re not saying that you shouldn’t consider switching to Sprint, but that Sprint should be more transparent about exactly what customers should expect.

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