6500slide is integrated with Carl Zeiss Lens, while 5610xm slide do not have that lens.
5610xm is integrated with Sound Chip as it is a music phone, while 6500slide doesnt have.
6500slide is made of aluminium (if i am not mistaken) so the price is more expensive.
Depends on what features u want .
New or Second hand? 6300, 6233 etc is good

for second hand, it should be around 450. Search for it.
k850i, LG Viewty, I-mobile 902, samsung g800 etc is good

Thanx for the recommendation on the 6300 & the 6233. Any suggestions on new models?