Bug 991573 - Copy improvements in Call Barring service through MMI

Yes, we definitely need to distinguish between call waiting and call barring. 43 is the code for call waiting and 33 the one for call barring. I think they're standard because they work in the same way across all my SIMs (from three countries no less) but it would still be better to figure out which standard they're part of. We tend to write that down in the code when we do some special-casing like that. Additionally I agree with Doug that those should become named constants, it improves readability a lot.