User interface design for a mobile device involves several issues. You should consider exactly what tasks your users need to accomplish. Are they monitoring inventory, recording sales, or inquiring about a customer's current credit status? Because the screen size is much smaller than a standard desktop computer, you cannot simply transfer your application from the desktop to a mobile device. Concentrating on specific user tasks can help you narrow down the information your screen should contain.
Ease of use is an important consideration in interface design. For example, keyboards on mobile devices are quite small and may be very difficult to use in the field. You might consider allowing users to choose options via check boxes and radio buttons in the device display area. If you still require an on-screen keyboard, be aware that it occupies valuable screen space.
Application operating rules are also different on mobile devices compared with desktop operating systems. For example, a PDA operating system allows only one application to be active at any one time. The user controls which application is active, and the system makes the previously active program dormant.