Homeserve, a home emergency insurance supplier, is to switch some 4,000 voice and mobile data connections to O2 from incumbent providers Orange and Vodafone.
Under the three-year deal, O2 will provide a VPN call routing service to ensure that calls are dealt with quickly and logged easily using a data connection.
The contract includes BlackBerry and PDAs as well as mobile phones, O2 said. Homeserve has more than 5,000 employees and sub-contractors across the UK.
Homeserve CIO Trevor Didcock said the network would give staff real-time updates on their PDAs and let them contact customers by SMS. "It will ensure we are delivering a first-rate service for our customers," he said.
Homeserve and O2 declined to provide financial details.