I had something similair the other day. Didnt check it fully as I am happy with what I have.
As for the phones well the W580i is a walkman phone so good if you like to listen to music (although I've read alot about this one breaking down) The K770i is basically the same but aimed at people who like to take pictures. The samsung is ok but looks horrible in my opinion. My dad had it and never had a problem with it but It looks horrible lol.
So basically if you like music go towards the W580i or if you like to take pictures go towards the K770i and if you like ugly phones go towards the Samsung lol. They can all do almost the same things TBH but some do it better i.e walkman, camera phone.
Some links to info on the phones if your intrested.
K770i
http://www.sonyericsson.com/cws/prod...overview/k770i
W580i
http://www.sonyericsson.com/cws/prod...0i?cc=gb&lc=en
U600
http://reviews.cnet.co.uk/mobiles/0,...9290093,00.htm