Verizon Wireless will replace its unlimited mobile data service with usage-based pricing for iPhone customers around the middle of the summer, according to the finance chief of parent Verizon Communications.

Verizon Wireless currently allows unlimited web-surfing for $30 a month for users of its version of the popular Apple Inc phone. But this will change in coming months.

We will probably do that in the mid-summer time frame, Verizon Chief Financial Officer Fran Shammo said during a webcast of an investor conference.

Verizon Wireless kept its unlimited plan for its first iPhone customers as it didn't want to put up a barrier to consumers who wanted to try out the device on its network, the executive said.

Verizon's February iPhone launch ended AT&T Inc's three years of exclusive U.S. rights to sell the device.

Shammo also appeared to hint that Verizon Wireless would add another iPhone to its product line-up later this year when he was asked about how iPhone would affect profit margins.

There could be some (margin) lumpiness when you launch the phone, the CFO said. If there happens to be a new one that comes out, that quarter might not look so good (either).

But Verizon Wireless, which pays a hefty subsidy for customers who sign up for two-year contracts, will still manage to report profit margins in the mid-40 percent range for the full year 2011, Shammo said.

Verizon Communications shares were down 2 percent at $36.18 in afternoon trading on the New York Stock Exchange.

(Reporting by Sinead Carew; editing by Dave Zimmerman)