Sooner or later, you'll be deciding on the type of GUI you'll be using in your flash application. One important consideration is the usage of vector versus bitmap images. On one hand, vector graphics, due to their mathematically derived functions, are able to be sized without much quality loss. However, when it comes to rendering vector graphics, it does take longer to render.
For bitmaps images, resizing (espeically in Flash) can be an issue since you will lose much of the quality of the picture. However, it is much easier for the program to render and animate.
So what's the trade? Obviously, it is quality and speed of rendering. To a certain degree, you can have the best of both worlds. Consider the following flash creation: It is a animated bullseye moving in a circular clockwise motion. Why a bullseye? Firstly, a circle contains the maximum number of edges per polygon. Moreover, creating a bullseye pattern multiplies the number of edges around 2 fold for each additional ring. The animation is recreated once in bitmap form and vector quality:
So what can you do? Yes, for complex, animated objects, bitmaps are better suited. However, before importing them, you can resize them using a photo editing program such that the quality is not lost. Moreover, after importing, you can right click the picture, choose properties and select the quality retained in the picture. By following these steps, your bitmaps can remain sharp and will decrease the load on your cellphone.
For vector objects, it's important to keep things simple. This means removing any unnecessary edges and corners in any shapes. Be sure to use the optimize feature (Ctrl+Alt+Shift+C) to decrease the corners and edges.