Sprint Nextel is taking on T-Mobile USA through its Virgin Mobile subsidiary by offering $100 in prepaid credit to T-Mobile subscribers who defect by the end of the May. T-Mobile said it felt no need to respond with an offer of its own. "We're not worried about it. Between the network, plans and devices, we feel good about what we've got," Senior Vice President Andrew Sherrard said. T-Mobile has increased traffic to its retail outlets since announcing its no-contract policy, according to Executive Vice President David Carey, who said it was too soon to arrive at any conclusions about the strategy.