A new lawsuit alleges AT&T is regularly overcharging iPhone and iPad customers for data usage, in some cases up to 300% more.

[ad#Google Adsense 300×250 in story]Lawyers for the lawsuit said they spent $80,000 testing devices in preparation for their day in court. In one instance, lawyers purchased a brand new iPhone and turned off everything that could affect data usage. When the bill came in from AT&T, there were 35 transactions for data usage, according to MSNBC.

Lawyers said that AT&T overcharged on every single transaction. Not once did a data usage charge go in favor of the customer. Lawyers said that AT&T systematically overstated data usage by 7-14% and sometimes up to 300%.

While they said that individual charges may add up to $10 or $15 a month, with millions of customers, it’s quite a boon for AT&T.

One lawyer compared the AT&T charges to a rigged gas pump where you pay for a gallon of gas and only get 9/10 of a gallon.

AT&T says the charges are “without merit” and says customers misunderstand how data is charged. The company points to things like automatic app updates in the background that customers may not be aware of.