WASHINGTON—Verizon Wireless said a new $350 fee that it charges some subscribers to break cell-phone contracts is necessary to cover its higher costs and the "risks" of offering high-speed wireless Internet service.

The wireless giant offered up a defense of its new fee—double the fee charged to other subscribers—in response to an inquiry by the Federal Communications Commission.

Verizon's higher early-termination fee applies to smart phones, including Motorola's new Droid. Getty Images

The fee applies to smart phones, including some BlackBerry models and the new Motorola Droid phone.

"The higher (early termination fee) associated with Advanced Devices reflects the higher costs associated with offering those devices to consumers at attractive prices, the costs and risks of investing in the broadband network to support these devices, and other costs and risks," Verizon wrote in a letter Friday to the FCC.

Verizon Wireless is a joint venture between Verizon Communications Inc. VZ 0.42% and Vodafone Group PLC.

An FCC spokeswoman didn't immediately comment on the letter.

Earlier this month, the FCC asked for more information from Verizon about the $350 charge for some subscribers who break their cell-phone contracts.

The letter was part of a broader inquiry the FCC has launched into competition and business practices in the wireless phone industry.

Agency officials are considering what, if anything, they should do to require companies to offer more information about the monthly fees subscribers pay and whether to impose new rules to help consumers who want to break cell phone contracts early.

The early termination fee is unpopular with many subscribers because it prevents them from dumping wireless providers that offer spotty service or who don't offer the latest must-have-it phones.

Last month, the Government Accountability Office released a report that found "early termination fees" were among the top four consumer complaints on wireless issues to the FCC from 2004 to 2008.

Several wireless carriers, including Verizon Wireless, AT&T Inc. and Sprint Nextel Corp. , pro-rate the fees so that consumers who break their contracts early don't have to pay the entire $175 or $200 fee.

Wireless carriers argue that they need to charge the fees to help recoup the cost of offering free or low-cost handsets to consumers. Consumers can buy phones at full price and subscribe to wireless services on no-contract plans, the industry says.

In its letter, Verizon said the termination fee also covers some operating costs of the business, including some advertising.

The agency is also looking into complaints about whether some Verizon subscribers have been getting hit with a $1.99 fee for inadvertently accessing Verizon's Mobile Web service.

Verizon said that the fee isn't charged if a customer "simply launches the Internet browser and lands on the Verizon Wireless Mobile Web homepage" but said that if subscribers believe they've been charged for "minimal accidental usage" they can call customer support and ask for a refund.

Write to Amy Schatz at Amy.Schatz@wsj.com