I regularly use my iPAQ 2210 with SysOnChip CF card antenna on Ryanair flights; I always ask politely, always start with "when the seatbelt warning has been extinguished, please can I...", always ask the senior cabin crew member, and always ask at a time when they are unstressed and without drill deadline.
Never declined.
If fortune indeed comes in to it, I hope you are as fortunate as I.