Cheap international calls

If it is someone you call regularly, then use your pc or mobiles via Messenger or WhatsApp which are totally free. If you are both Skype users, then that is free too.
Otherwise you need to look at options from your phone supplier for international packages. Or buy Skype credit. It all depends on who you are calling, which country and how many minutes.

WEZEMBEEKWANDERER
That is NOT good advice....can someone please answer this question, it is a good one. A good international call plan/company when you need to do business or make long calls to banks and companies etc overseas. One option is to create a VOIP Account. Your phone will use it's data to make the calls and the VOIP Company may charge something like 3 euros a month plus .09 euro cents a minute or something like that.

@ PARADOX, what on earth is wrong with WEZEMBEEKWANDERER's advice. It's perfectly sensible. It's actually a lot more specific and usable advice than your own answer.

I've got to agree that WWs answer is perfectly good answer.
Paradox assumes that the calls are to be made to 'banks and companies etc' and there is nothing in the question to suggest that this is the case.

That said, you need to give far more information to get a definitive answer. Where are you calling, what time of day and are your calls to private individuals or businesses? (Skype and WhatsApp are likely to be less useful for business calls.)
I use Proximus. They offer free calls to any one of a range of countries if the calls are out of normal business hours on Monday to Friday and €1.00 per call - no time limit - during Belgian business hours. I understand that Telenet offer a similar service to a wider range of countries but that Telenet is not available over the whole of Belgium. I opted for calls to UK so any business calls are free from 16.00 UK time.

@PARADOX
Both Skype and WhatsApp are VOIP applications.
One might conclude from your contribution that you've been listening to people who know what they're talking about without understanding the jargon. Or "something like that".

VOIP calls are cheaper...
Depending on the country you wish to call the rates vary...
Bear in mind the cheap rates are not necessarily the cheapest ( some charge connection fee for every call)
http://www.voip-comparison.com/
http://www.voipratetracker.com/compare_rates

Select the country and the service ( Fixed line or mobile call or SMS) and you get the rates for different voip providers

Check out Skype subscriptions. World plan is €16/month unlimited calls to landlines in over 60 countries.

REBTEL is very cheap.