iPhone 3GS unlocking problems

[Jbinspain]

Hi; as I've never owned one of these before, please excuse any obvious questions, or remarks. I have an iPhone 3GS that was my son's old phone. It was locked to Orange Uk. I had a software unlock done, but was told that the only way to do this was to take the software back to ios 4.1 and that if it was subsequently attempted to update the software to the latest iOS 5.0 then the phone would automatically become locked again. In most cases, this is not too much bother, but it is inconvenient in that certain apps cannot be downloaded as they require ios4.3 or higher. Is there any way around this problem, without risking locking the phone again? Thanks.