contract help?3, O2,T-Mobile..? this is the first time i am thinking and prone to take a mobile phone contract..and i want to take something that i wont regret later.

I am CONFUSED!
I have to choose one from these mobiles on offer from 3 network UK....only to be able to use SKYPE for free and the 3G facility of this network.
which one is best? in all terms..camera, battery life(since i'll be using mostly for calls) ;-)..music playback, stereo?
I am just confused! and do i really have to get into a contract to use the free skype service from 3?
I was thinking of buying a Windows mobile which has wifi..but the cameras are not so worthwhile..2MP
or do i just take the basic N73 on £15/month on 3? well..its an old phone
Is it possible to use SKYPE on other UK network..I mean, if i take a mobile on O2 for example?
which is the best network for these services??

thanks for helping