New 16GB 3G White Sim Free Unlocked Mobiles

[funkylad20]

I have a 16GB 2G mobile which has been 'jailbroken' to allow me to use my own 02 Sim in. Works fine but am considering an upgrade to the latest white 3G version.
I notice they are for sale unlocked (Play.Com = �599) BUT can anyone tell me:
1) Can the phone be used in same way as contractually bound O2 mobile (i.e. Download applications, iTunes etc.)
2) Will there be a warranty with the phone?

Curently I use my iPhone in many ways but cannot access any decent apps like 'normal' iPhone as was told if I plugged it in anywhere it would render my phone useless!