You can use the idle url to display a custom logo which can be composed of text, custom softkeys, and pictures (special "cip" black/white images for 7940/7960 and color PNG images for 7970). You can have set the idle url as an enterprise parameter or on individual phones, so you can have color logos for your 7970's and CIP images for other phones (and some phones may not use the idle url at all, if you configure it that way).