Hah, just reminded me..

My daughter, whilst roaming in the US from the EU somehow managed to get unlimited data after her initial miserly roaming allowance was used up.. simply by switching airplane mode on and off repeatedly until data worked.

I was stressing getting back home to a huge bill, but kept the "all chargeable services have been stopped" messages just in case.

My final bill was £300+, zeroed.

Phew!