all phones have more or less the same features connectivity wise...bluetooth,IR etc etc
6230 has EDGE...6600 doesnt...not sure abt 7610
all have 65k colour TFT screen.....but 6230's screen is too small, i personally dont like it...6600 has an excellent display(2.1" diagonal)
7610 has the best camera ofcourse...1 MP..lets u capture pics to a resoltn of 1152x768....6600 and 6230 have a standard VGA cam, res of 640x480
of course 6230 is the smallest and lightest and most easy to carry around...
depends upon ur priorities