it says "call cannot be connected, please check your phone settings" when i tried to make a call using iphone 4s

I am from the US and have T-Mobile as my carrier. I have no problem making phone calls in the US.

I am in the Philippines now and have problem using my iPhone 4S when I tried to make a phone call. I hear a recording that says "call cannot be connected, please check your phone settings". I did "Reset All Settings" to no avail. I still cannot make a phone call. How do I solve this?

I did not have a problem last year when I was in the Philippines.