Federal regulators are asking Verizon Wireless why it recently doubled the fees it charges customers when they break their contracts on some of their phones.

In November, the carrier hiked its early contract termination fee for "smart" phones to $350 from $175. Like other carriers, Verizon subsidizes the cost of the devices to contract-signing customers, and smart phones cost the carrier more than regular phones.

The Federal Communications Commission is also asking the carrier if it charges those who accidentally hit Web access buttons on phones that have no data plans. Customers have reported repeated $1.99 charges when hitting the wrong buttons. Verizon says it ended those charges a few months ago.