Get a local SIM card from the country where you live, which I think is UK, or is it Portugal? A bit confused there, either way get a number from the country that you live in, make that your permanent and get a local SIM card to wherever you get sent for assignments.
International SIM cards are kinda crap. There used to be one called SIM4Travel, but that went out of business. I have one from WorldSIM, and it's horrible. Their customer support team doesn't even understand basic terms and their service doesn't work very well outside the EU and the UK.
My dad has one too and he tried using it in Nairobi, UAE and Qatar, calls kept dropping and sometimes I wouldn't be able to call him either, it'd go straight to voicemail instead.