yes dude u can flash k550im to w610i easily..
but u will loose the speed of imode.. u will then have normal EDGE connection !!
i have guided ppl to flash their k550im to w610i with success

just google search flash k550 to w610 and read the tutorial !! ;)

u hv the following options

w610i Main and k550im FS ( old no flashing FS)
w610i Main and w610i FS ( recommended )

to revert back u will need use SEUS.. to flash k550im main
and if u flashed w610i FS also then u must flash back k550im FS ...