The deal gives the mobile phone retailer the flexibility and responsiveness it needs to shift from selling mobile phones to earning more from telecoms services, said CTO Simon Post.
Carphone Warehouse will also licence Patni to resell to new virtual network operators a customer relationship management (CRM), billing and provisioning package that is effectively a "telco in a box", Post said.
He said the decision to outsource and offshore left Carphone Warehouse free to respond to the needs of the business. "Things happen so fast here that a three-year IT strategy is out of the question," Post said.
"We concentrate on building an infrastructure that helps the business respond flexibly and quickly."
Post said the deal cemented a "four or five-year ad hoc relationship" with Patni. Patni helped to develop Carphone Warehouse's CRM billing system, and looks after several of the retailer's legacy systems that cover insurance and other business lines.
Carphone Warehouse is also likely to work with Patni to redevelop its customised electronic point of sale system, said Post. This currently runs on Digital Alpha technology under VMS and serves more than 2,100 stores in 11 countries.