T-Mobile earned a huge amount of goodwill from consumers last month when the carrier announced it would be giving away 200MB of free data to all tablet owners. But the company has stumbled somewhat in implementing its generous offer. And it's taking criticism for failing to make clear one important exception: any customer buying a new tablet through T-Mobile's attractive $0 down financing won't be eligible for truly free data.

One requirement when financing a tablet is that you maintain "a paying service agreement" with T-Mobile from month to month. In layman's terms, that means you'll need to sign up for a postpaid (but contract-free) account. The cheapest way to do that is to opt for a $20 plan that includes 500MB of data. The 200MB bonus is added on top of that, so all told you'll receive 700MB of monthly data to burn through on your device.

Customers financing a tablet will need to pay monthly for "free" data

"We are happy to extend credit to you for a device with a value of several hundred dollars, but we do require that you establish a paying service relationship with us," reads a new press release from T-Mobile that seeks to clear up any confusion. For anyone buying a new iPad Air (or any tablet that works on T-Mobile's network) outright, you'll get 200MB of free data every month just as promised.

But for everyone else, there are still no strings attached

There have other teething problems with the new offer. Some customers who tried to take advantage of the offer at launch were told that they'd need to spend at least $10 monthly for the free megabytes. T-Mobile has an explanation for this, too. "We had an executional error in our system at launch that created an erroneous $10.00 charge for network access." The carrier says it's worked to rectify the program on its website and ensure that retail employees understand the policy as intended.

CEO John Legere has issued a couple of backhanded apologies in the process. "Our bad!" is a strange way to acknowledge that your no-strings-attached free data offer does actually have a string attached, but Legere has frequently proven to be a strange CEO.