In his first major speech since taking control of Yahoo last June, Mr. Yang announced the launch of a new upgraded mobile home page for cellphones, an updated version of its mobile portal Yahoo Go as well as new software tools to help outside developers design applications and widgets to work in conjunction with Yahoo’s mobile offerings. Yahoo also announced new partnerships with News Corp.’s MySpace, eBay Inc. and Viacom’s MTV network, which will see those companies use Yahoo’s development tools to create mobile applications users can access through Yahoo.