It is easy to change the screen size of the Screen Designer in NetBeans Mobility Pack. Right click on the Screen designer and select Screen Size from the popup menu.
You will see immediatelly the change of screen size in Screen Designer but when you run it on the emulator the emulator screen size is still the same.
To change emulator screen size you'll have to change the properties of the emulator. They are in [EMULATOR_INSTALL_DIR]\wtklib\devices\[EMULATOR_NAME]\[EMULATOR_NAME].properties There is plenty of properties in this file. We are interested only in following properties. They are distinguished by red and green color on the picture.
It will allow you to change the visible area of the device. The result can look a little bit strange because the display area is still the same only the painting is done into the are that you defined. You can find more informations how to customize or create new device emulator in BasicCustomizationGuide.pdf document in the Wireless Toolkit [WTK] docs directory. Note: this document isn't distributed with WTK bundled with Mobility Pack
Source: Lukas Hasik's Weblog