I'd say mobile search and mobile web services, since Yahoo Japan was/is a legitimate joint venture by Softbank and Yahoo where they started it from the ground u

I'd say mobile search and mobile web services, since Yahoo Japan was/is a legitimate joint venture by Softbank and Yahoo where they started it from the ground up, and the services being pre installed on Softbank phones made a huge strategic impact on user adoption. They are the low cost leader in mobile telephony, have a vast solar operation (heavy govt subsidies), and have a powerful contract software Salesforce.