NYS secured the deal after a competitive tender and will also provide a "small meetings management service".
Cost-control was one of the key elements O2 was looking for in a market sure to be affected by price rises ahead of the 2012 Olympics.
"During the competitive process, NYS Corporate stood out as offering a clear cultural fit," said O2 category marketing manager Allison Webb.
"They also provide clear, transparent ways to control and reduce spending."
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