Verizon Wireless was apparently the first major carrier to make an “unlimited” plan available nationwide with no domestic roaming or long-distance fees. Its announcement was all but five hours old when AT&T announced its own unlimited plan.

“This is a highly competitive market, and we’re committed to moving fast to meet customer needs,” said Ralph de la Vega, chief executive of AT&T Mobility.

Three hours later, T-Mobile followed suit, saying it would introduce a $99.99 plan Thursday. Unlike the Verizon Wireless and AT&T plans, T-Mobile’s includes unlimited text and picture messaging, which costs $14.99 per month when added to other T-Mobile plans.

The Verizon Wireless plan is “likely to have repercussions for years to come,” Sanford C. Bernstein analyst Craig Moffett wrote in a research report, before the other two carriers introduced their competing plans.

Moffett likened the Verizon Wireless move to Sprint’s introduction of 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.

A relatively small number of cell phone power users are expected to benefit from the new plans, but investors saw little chance for the carriers to recoup lost revenue by up-selling customers who now pay less.