If the back is mostlly metal, with a black strip of plastic on the bottom, it is a 1st Generation iPhone. If the back is contoured, and solid black or white with a silver apple, and grey text on the back, you have an iPhone 3G. If the back is contoured, solid white or black, and has a silver apple, and silver text, you have an iPhone 3Gs. If the back is completelly flat, and solid black or white, you have an iPhone 4. Could you post a picture of the back of your iPhone?