I see Vodafone have launched their Blackberry PAYG range and offering free BIS untill June 2011.
You have to pay for your calls texts and internet. But you get free BBM, Facebook, Twitter, possibly IM and email. Which for those in LDR or away from home maybe useful..
Of course please check for your self the latest on this offer as im sure it can change etc..
One thing i found out is you can use your existing sim so can keep your number..