Esri offers users a host of solutions, designed to be used from PC, web and mobile clients, however, lately there’s definitely huge interest in the mobile ecosystem. The company actually offers 5 solutions they bill as “mobile” offerings. These include ArcGIS for Win Mobile, ArcPad, ArcGIS for Windows Phone and ArcGIS Desktop – each has it’s benefits, price point, and target audience/user.
From Esri… Each of these technologies provides a specific set of capabilities that meets the needs of different end-user application requirements. Trade-offs in software and hardware capabilities, mobile OS, price, size, device ruggedness, and battery life help determine which of these Esri technologies are best suited for your organization’s size, workflow, project scope, and/or development scenario.
For a little more clarification on the mobile solution offerings you might check out this recently published Q&A