Mobile US and Sprint said Sunday they believed they could win over skeptical regulators to their $26 billion merger because it would create thousands of jobs and help the United States beat China to creating the next generation mobile network. The agreement capped four years of on-and-off talks between the third- and fourth-largest US wireless carriers, setting the stage for the creation of a company with 127 million customers that will be a more formidable competitor to the top two wireless players, Verizon Communications and AT&T.