"These customers would normally have been billed at the standard rate of $1.99 per megabyte for any data they chose to access from their phones," the company said in a statement. "The majority of the data sessions involved minor data exchanges caused by software built into their phones; others involved accessing the web, which should not have incurred charges. We have addressed these issues to avoid unintended data charges in the future." The problem has been occurring since at least 2007.
The refund will be in the form of $2 to $6 credits, though some will receive larger funds, on the customer's next bill (unless you've left Verizon in the meantime, in which case you'll get a check in the mail). Doing some simple math (credit amount multipled by number of customers affected) shows that the company will pay out somewhere between $30 million and $90 million in total reimbursements.