Pre-paid sim cards working overseas?

Does anyone know if it’s possible to use pre-paid sim cards in phones while overseas ? ( I have an IF card in my mobile here )

My wife has an If card. It don’t function in Philippines.
So i suppose your card will not work abroad.

My FarEastTone prepaid worked in Hong Kong. My wife’s MobiTai account one didn’t. It depends on what sort of deals they have with foreign carriers, etc…

Is it a case of having to contact the company before travelling ? I had to do this when I left the UK to get my UK pre-paid card to work here in Taiwan.