A while ago I read somewhere that you could greatly improve your photographs by removing the small plastic lens cover on your Desire (as suggested above) and replacing it with a cut-out from a photographer's lens filter - these can be really cheap (less than £5 for a 77mm diameter UV filter) and can be cut into several lens-cover-sized pieces. If you get a scratch, you just replace it.
It could also do some interesting things for your photographs, especially if you experimented with different filter effects - polarising, UV, ND etc... could be good fun if you're feeling artistic.
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