I live in Guernsey so I can't have an iPhone on O2 and was wondering if I bought an unlocked iPhone, what problems would I come across?

I've been told I won't be able to download software for it from iTunes as it will become locked again...

Could I instead download 3rd party software for it?

What would happen if I try to sync music from iTunes to my iPhone?

Would I still be able to put films and music on it from say Windows Media Player? Or is the iPhone locked to only work with iTunes?

Would I still be able to use all the features on it?

Thanks