Blackberry - how to resize image?

You can do this pretty simply using the EncodedImage.scaleImage32() method. You'll need to provide it with the factors by which you want to scale the width and height (as a Fixed32).

Here's some sample code which determines the scale factor for the width and height by dividing the original image size by the desired size, using RIM's Fixed32 class.

public static EncodedImage resizeImage(EncodedImage image, int newWidth, int newHeight) {
    int scaleFactorX = Fixed32.div(Fixed32.toFP(image.getWidth()), Fixed32.toFP(newWidth));
    int scaleFactorY = Fixed32.div(Fixed32.toFP(image.getHeight()), Fixed32.toFP(newHeight));
    return image.scaleImage32(scaleFactorX, scaleFactorY);
}

If you're lucky enough to be developer for OS 5.0, Marc posted a link to the new APIs that are a lot clearer and more versatile than the one I described above. For example:

public static Bitmap resizeImage(Bitmap originalImage, int newWidth, int newHeight) {
    Bitmap newImage = new Bitmap(newWidth, newHeight);
    originalImage.scaleInto(newImage, Bitmap.FILTER_BILINEAR, Bitmap.SCALE_TO_FILL);
    return newImage;
}

(Naturally you can substitute the filter/scaling options based on your needs.)

Just an alternative:
BlackBerry - draw image on the screen
BlackBerry - image 3D transform