JumpTap, the Cambridge, Mass. mobile Web services company, has raised a $26 million D round. JumpTap makes mobile Web portals for carriers like AT&T (T) and U.S. Cellular (USM) and sells mobile ads for carriers and publishers, including NBC Universal (GE).

JumpTap will use the money to continue developing its products, hire more sales

Mobile advertising is supposed to be a huge market, some day. But even those predictions pan out, it won’t be easy for JumpTap: Beyond other mobile ad upstarts, it’ll increasingly be competing for deals with the likes of Google (GOOG), Microsoft (MSFT), and Yahoo (YHOO).

AllianceBernstein (AB) led the round; all existing investors also participated, including General Catalyst Partners, Summerhill Venture Partners, Redpoint Ventures, Valhalla Partners, and ad conglomerate WPP.