Long Island Rail Road customers will be able to use their smartphones to buy a ticket to and from anywhere in the system by the end of next month — four months earlier than originally planned, officials said Tuesday.

Gov. Andrew M. Cuomo joined Metropolitan Transportation Authority officials in Grand Central Terminal to announce the streamlined rollout of the agency’s new eTix system, which will allow riders on the LIRR and Metro-North to buy and display tickets using their mobile devices.

The system became available to customers on the Port Washington branch last week, but was not originally scheduled to be available systemwide until the end of December. MTA Chairman Thomas Prendergast said Cuomo “challenged” the agency to move up the rollout.

“This e-ticket system for the railroads is where the economy is now,” Cuomo said. “You take out your device, you scan, you pay for something. That’s how it works, and that’s how it’s going to work on the railroads.”

The eTix app, created by London-based app developer Masabi Ltd., will be available systemwide on the LIRR and Metro-North by Aug. 22, allowing customers to select the type of ticket they want to purchase, save it in an “electronic ticket wallet,” then activate it when boarding a train. A customer displays the activated ticket screen to a conductor.

“You’ll be able to buy your ticket before you leave the house, on the way to a station, or wherever and whenever you want,” Prendergast said. “And that means greater convenience and freedom than that which you have experienced in the past.”

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At Penn Station Tuesday, Massapequa commuter Kevin Bonora said he was excited at the prospect of being able to buy tickets on his phone because it makes it less likely that he’ll lose his ticket.

“That would definitely be a step in the right direction,” Bonoran, 24, said. “We could do with an upgrade.”