A complaint has been filed in a federal court in California alleging that AT&T regularly and purposely overcharges iPhone and iPad customers on capped data plans by inflating the amount of data they download to their devices. The complainant, Patrick Hendricks, says that AT&T adds “phantom traffic” to its invoices in order to overcharge users. “AT&T’s billing system for iPhone and iPad data transactions is like a rigged gas pump that charges for a full gallon when it pumps only nine-tenths of a gallon into your car’s tank,” the complaint alleges. Hendricks’ lawyers hired a consulting firm to investigate the matter, and it apparently determined that AT&T regularly balloons data activity by between 7% and 14% — adding that the carrier sometimes overstates data totals by as much as 300%. AT&T said it would fight the lawsuit “vigorously” in a statement to Computerworld.

[Via 9 to 5 Mac]