ok, i have both the iphone and BB bold, so...
BB sim in iphone = no issues
iphone sim in BB = limited features etc.
so ask o2 to enable the BB features on your subscription, strongly suggested. :D check
O2 – The UK's Leading Provider of Mobile Phones, Broadband & SIMs for details about their prices though, i think they might be different to the advertised ones because you already have the iphone contract.