The company promised to add Wi-Fi services to its entire electric and diesel train fleet when it renewed its licence in May 2005.
"The fleet was due to be complete in May 2007, but in response to popular demand from passengers, GNER has speeded up the project and all of its trains will offer Wi-Fi by the end of this summer," said a company statement.
GNER's fleet of 11 diesel trains is currently being fitted with Wi-Fi equipment at the company's Craigentinny depot east of Edinburgh.
The trains send and receive communication signals using a combination of a roof-mounted satellite dish and mobile phone antenna using 3G and GPRS technology.
Each coach along the entire length of the train is then connected via the onboard wireless network to create a Wi-Fi 'hot-spot' in every coach.
First Class passengers can access the service for free, while in Standard Class the system operates on a 'pay-as-you-go' principle, similar to an internet café.
"Wi-Fi offers immense potential for business and leisure passengers, and the feedback we're getting as the technology spreads across the GNER fleet is very encouraging," said GNER chief operating officer Jonathan Metcalfe.
"When the whole GNER fleet is Wi-Fi equipped, we will operate Britain's first all-Wi-Fi train fleet."
GNER was the first UK train operator to use Wi-Fi technology to provide uninterrupted internet connections for passengers.
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