Any old stylus won’t work on a device with a capacitive touchscreen as found on the HTC HD2, Nexus One, or iPhone. Instead, you need a special capacitive stylus such as one directly from HTC (for about $25). Or, if you want to save some cash, you can get a capacitive stylus from eBay for less than $5. As mentioned in this video, the advantage to having a capacitive stylus is that you can use your phone with gloves and you can have more precision when using a drawing or handwriting recognition program on your mobile device.