Re: i am going out of the country and have changed to international calls.
i cannot make phone calls
As almost everyone said, you either do not have an international plan and your phone must be locked.
I am not aware of the international plans, but I know that the roaming fees are mind-blowing. Your best option is to unlock your phone. Now,
the ways you can unlock your phone are different, because you didn't mentioned that phone you have? If you do not have an iPhone, then I
believe that you can get an unlocking code either from the network company you are using or with an unlocking tool (I do not know many things
for non-iPhones). If you have an iPhone, then you need to take into account your iPhone model, your iOS version, your network, your IMEI
status, etc...
I found two very good articles, one for Android/Windows phones and one for iPhones. I suggest you should read them:
Android/Windows phones: Unlock phone: How to use any SIM in your phone - unlock iPhone or Android and save money - PC Advisor
iPhones: 3 Methods on How to Unlock a Locked iPhone