Re: i am going out of the country and have changed to international calls.
In the event you did setup international service on your plan as Just Me, D suggested; I'd call or email/chat with your carrier to be sure everything is configured correctly.
On one trip to the UK/Ireland I landed at Heathrow and had no service even though I setup an option for SMS/voice with my carrier. Took several email exchanges to figure out that my carrier had programmed international service for a SIM that I no longer had. The phone I had (BlackBerry Bold) at the time was configured correctly in the carriers system - just not the SIM.
I think that's the ideal option. Have done this for Asia trips. Just get a local SIM at the airport, or what I did was to pre-purchase a local carrier's SIM ahead of time with minutes already provisioned and ready to install in phone upon landing. Worked well.
If your sim has service in the foreign country and still unable to make calls, the format in which you have saved numbers could also be an issue. You need to prefix numbers with the correct country code, etc etc.
I am going out of the country and have changed to international calls. Why ca...
Depence what country you bought your iPhone. UK stores sells "unlocked" till first sim. What you operator sim you put first than iPhone will be locket to that network. I dunno about other countries. Second if you can't get work local sim or you phone isn't unlocked than turn on calls, messages roaming this will let you make calls and txt messages sent to peoples.
Third all numbers must start with +(country code)(phone number) or 00(country code)(phone number)
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