Doesn't look that straight forward to me , check out...

Doesn't look that straight forward to me , check out http://www.starhub.com/personal/support/mobile/roaming/prepaid-roaming/happy-roam.html

You need to have a minimal balance and if you shoot out of your quota it goes back to standard roaming rates (eating up your balance). Only limited to Starhub customers and I also noticed that it does not have calling capabilities.

I doubt the air crew will go for it because you physically need to change sim each time you travel. Flexiroam X gives the crew the convenience of not having to change sim , wide coverage and easy to recharge.