Pinatubo.

Are you sure that it is the FS system not accepting your changes? Or is it that those call signs may not be included in the ATC voice pack?
Sometimes if you don't add it correctly, it isn't accepted. I think it's could be like this "speed bird" is accepted, but "speedbird" is not (or the other way around, I'm not sure at the moment). Do you get my meaning?

When I first got the CS 757 I looked up all the airline call signs and added them to the ones that weren't there. In the end, most still weren't working. Next I added them to the list in the airlines.cfg in FSX root folder and they still weren't working. I never tried it again after that.

Mark