Can I get a Micro SIM for an unlocked iPhone 4S?

I have a Blackberry but would like to now get an iPhone. I can't upgrade until 2014 and so I will buy an unlocked iPhone. My question is; can I get a micro SIM from Orange even though i'm still in contract with them for the blackberry?

Yes of course you can! Just don't tell them you're on contract with them, even if you do - it won't no matter.

Anyone in an Apple store will be more than happy to get a micro sim for you for free, no questions asked, no matter who your provider is
they'll help you set up your iPhone too if you ask

Yes or you can buy a sim card cutter from ebay so you can put your blackberry sim in it.