(CNN) -- Verizon Wireless said Sunday it will give refunds to about 15 million of its customers because the company incorrectly charged them for data sessions.

Over the past few years, some 15 million Verizon customers who did not have data plans were billed for sessions on their phones that they did not initiate, said Mary Coyne, the company's deputy general counsel, in a statement.

She added the majority of data sessions involved minor exchanges caused by built-in software. Others involved opening the web, which should not have incurred charges, she said.

"We have addressed these issues to avoid unintended data charges in the future," Coyne said. "Our goal is to maintain our customers' trust and ensure they receive the best experience possible."

Current customers will receive notification of credits on their October or November bill of between $2 and $6 in most cases, while former customers can expect to receive a refund check in the mail. Some will receive larger credits or refunds.