game-editor.com

well, how do you?

Learn how to use GE, and be sure that once you start designing for those devices, you start with a correct game/screen size, know the memory limits of that device and use graphics/sounds in accordance, and when it's done you export it to said device.

Actually, the answer isn't nearly that simple. First of all, Game Editor only supports Windows based mobile phones. If you want to develop for any other type of cell phone, I suggest you learn J2ME (Java Mobile Edition). You also cannot use Game Editor to write games for Palm Pilots. For that your best bet is to learn C. Note that you most likely will not find drag and drop development environments for these two segments of the mobile market. And if you do please let us know, because I'd like to see them.