I guess I'm a bit late to the conversation
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So, this is what I was thinking, Wi-Fi is useful, but, I guess I won't use it as much I would like, on the other hand what I'm surely going to use is GPS if available. Also, GPRS and 3G(when/if it becomes cheap) will be heavily used. On the multimedia front, C510 is probably better than the rest in less-than-13K range.
With about 13K as a budget, I would like to get a good device with GPS(and Symbian will be a plus) and the rest of the features being above average. Or, I will just buy the C510 and save some money and buy a decent headphone.