Verizon Wireless introduced an unlimited calling plan Tuesday with no roaming or long-distance fees for $99.99 a month, an offer that could spark a price war among carriers. Other major carriers have "unlimited" plans, but Verizon Wireless appears to be the first to make one available nationwide. The plan is "likely to have repercussions for years to come," Sanford C. Bernstein analyst Craig Moffett wrote in a research report, adding that in the short term, it will force Sprint Nextel Corp. to match the offer.

Sprint already has an unlimited plan that costs $119.99 a month, and includes unlimited Web use, e-mail and messaging, which Verizon Wireless' offering does not. But Sprint's plan is available only to residents of Philadelphia, Minneapolis, Tampa, Fla., and parts of Northern California.

Helio LLC, a small carrier that rents time on Sprint's network, is offering a $99 monthly unlimited plan nationwide. It includes unlimited Web use, e-mail and messaging. SK Telecom Co. of South Korea owns a majority of Helio.

Moffett said Verizon Wireless' move is a blow to confusing pricing plans, and likens it to Sprint's introduction of a flat-rate long-distance prices for landline phones in the 1990s. That made it easier to compare plans and hastened a rapid decline in prices, Moffett said.

Verizon Wireless also introduced a $39.99-a-month plan for cellular broadband using PC plug-in cards. Compared to the existing $59.99 plan, it's capped not by download speed but by the amount of data the user can download in a month: 50 megabytes instead of 5 gigabytes.

The $59.99 data plan was earlier marketed as allowing "unlimited" downloads, yet Verizon Wireless disconnected some customers for "excessive" use, a practice that resulted in a settlement with the New York attorney general last year.

Verizon Wireless is a joint venture of Verizon Communications Inc. of New York and Vodafone Group PLC (VOD) of Britain.