Some credit card companies will think an International charge is fraudulent and suspend your card until they can get in touch with you and confirm the charge. Just basic fraud protection.

But if you are travelling abroad and especially in flight, they might have trouble reaching you. Hence, your card will not be active the next time you try to use it.

I always recharge my Skype account from home because the CC company that I have linked to the account ALWAYS calls within 10 minutes of the charge.

If you let the CC card bank know in advance that you will be abroad, they will typically accept charges from the countries you will be in for the period that you say you will be travelling.