I have an iPhone 3G with a hard case on it. It is similar to the case in the link below:
Shiny Blue Hard Case for iPhone 2G 3G Screen Protector on eBay (end time 21-Sep-09 22:55:29 BST)
I am having trouble finding a windscreen mount for the car that I can use without taking it out of the case. There are some of the "gripper" ones I have found but I am not that fond of them as they are big and chunky and detract from the slim iPhone. There are plenty of other kinds in Ebay, but I am not sure if they will fit with the case still on.
If anyone has any experience or advice from a similar issue, I would be grateful for any pointers.