Question about iPhone sim and BIS. Orange UK

[ste1164]

I have an iPhone 4 and I have recently purchased a BB. I am on orange PAYG so I get the 250MB free every month. I want to put on BIS for my blackberry. If i ask orange to add the BIS will my 250MB free each month be removed or will it stay there?

[TomWilliams]

As a Voda customer I have a 500MB data bundle and the BIS add on as a seperate add on, therefore if i swap my sim to something else I still have 500mb

[ste1164]

Would the separate add on remove my 250MB though?