Hi
Can only tell you about Virgin as each airline is different.
At VS you start as econ cabin crew, then get promoted to "Senior" (working in the upper class cabin), then C.S.S (used to be Purser) and finally F.S.M (in-charge).
There are loads of office based jobs like rostering and crewing and crew support managers etc.
On board promotion is now all done on "performance monitering rather than length of service so if you were really keen, you could in theory be F.S.M in about 3 years....but that's a whole other thread!!!!!!!
Hope this helps and any questions, feel free to P.M me! x