Re:User-Agent = breakage (Score 1)

The User-Agent is about the only consistent way to recognize a mobile device. The accept headers don't reflect the device capabilities 99% of the time. SOMETIMES a UA-Profile header is available which is supposed to link to device capabilities, but often that is missing, the link is dead, or the link points to the capabilities for a different phone. The reason for actually needing to know the specific device is not for standard web pages ( a waste of your phone ), but for delivering content such as wallpapers, ringtones, or videos that are actually in the size and format supported by your device. Once again this is never consistent across phones.