A new study suggests that wireless carriers might be overcharging customers for monthly data usage. It’s an important study now more than ever since many wireless providers are moving away from unlimited data plans as a direct result of the increase popularity of smartphones in the US.

A team of researchers led by PhD researcher Chunyi Peng monitored two unnamed mobile providers in the US. Peng wouldn’t reveal the identity of the carriers but said collectively, they account for half of all US wireless subscribers. They used a data-logging app on Android handsets to measure how much data use each carrier was recording.

The researchers discovered that carriers usually counted data correctly but they tend to overestimate usage. Even with typical use, data use could be inflated by five to seven percent. This was particularly evident when streaming video or audio and when phones were used in areas with poor coverage.

Data overages, of course, could ultimately lead to excess charges for the customer in the event they were already on the edge of going over the limit on their data plan. For reference, both AT&T and Verizon charge customers $15 per extra gigabyte of data used. Their research found they were billed for 450MB of data that ultimately was never received.

The problem is that providers charge for data the minute it leaves their network regardless of whether or not the customer receives it. For example, if you’re streaming a video or music on your phone and briefly pass through a no-coverage zone, you’ll still be charged for that data despite the fact your handset never received it.

Peng said it should be easy enough for carriers to tweak their system but they might not believe they are responsible for doing so.