The O2 mobile network, owned by Telefónica, has outsourced its critical online applications for sales and customer service to Cognizant.
Under the "multi-year" managed services agreement, Cognizant will provide business and operational support to the phone service provider's online applications and "enhance its agility, flexibility and responsiveness to consumer demands and market changes", said Telefónica UK.
The applications perform a wide array of functions, ranging from promoting and providing access to Telefónica UK's products and services, to delivering end-user self-service functionalities.
Telefónica UK said the deal would help increase customer loyalty, expand its customer base, drive innovation, maximise returns on IT investments, and "boost competitiveness by balancing cost, complexity and capacity".
Brendan O'Rourke, head of online, integration and product design at the company, said: "Through this relationship, we will have access to Cognizant's global delivery network, industry leading practices and innovation."
The length of the deal and its value has not been disclosed.