I also have bought the Z610 no more than a month ago and I'm totally in love with it. before this one I had a Nokia (piece or crap) 3100. Then, my girlfriend got the Z520 beacuse she had seen it and liked the looks of the white model. To my surprise that phone was great! I still consider it one of the gratest phnoes abailable, if only I had a memory slot there would be no match for it.
In the end, looking for a similar phone, clamp(because its more sofisticated) the one I considered the greatest in comparison, even though it doesn't have IR nor external color display was this Z610. It is really great, the camera's resolution is exellent considering it is a Mobile phone. And the looks of the black one (the one I've got :P) is great. the only negative thing i see in it is that it is a magnet for fingerprints and keeping it nicely clean involves rubbing it constantly.