Prepay in Serbia, and Montenegro
 

What's a good "SIM card pack" to purchase for calling local mobiles in Serbia, and then Montenegro. It would be nice to keep the same number as I travel throughout the Balkans this summer (3month trip). In Norway, I found Chess startpacke which was great because it cost only 100kroner, and included the same amount of airtime credit. I use it sproadically, and 3 months later (in Sweden, and Denmark) I still have the same number, and have needed to top up. I guess what I'm asking for is a similar setup for the Balkans. The most important factor is price/minute, and coverage in rural areas. Thanks.