Mobile phone - Pay As You Go (Kuala Lumpur)

Hi Guys,
Will be in Malaysia for 3 months from mid July, I have 2 iPhones one is 3GS & the other is an iPhone4 so need Regular sim & a Micro sim (both phones are unlocked).
I was planning on just picking up a Pay As You Go sim card in the airport or somewhere and topping it up as and when needed.

Someone mentioned to me that I might have trouple with this plan due to them being iPhones & that they might need to be Jail Breaked?

Can anyone let me know if my plan is OK and if not surley I would be able to buy some cheap Pay As You Go phone in KL to use?

Thanks
Ben