Http://en.wikipedia.org/wiki/Belgrade Belgrade is the capital of Serbia. On this Wikipedia website on the right hand side a little ways down it lists the postal code as 11000. I don't know what you'll do with that, but I hope that helps.
The area code that I found is 202 let me see if I can locate the page I will post it 4 you
Go to the website maintained by the Post Office there and follow the directions.
I've listed the English language link. It's only a click away from seeing everything in Serbian instead.
I've listed the English language link. It's only a click away from seeing everything in Serbian instead.