You want to call the US from your cell phone? That will be expensive...

If you will have internet, you might consider Skype. If you won't have internet, just go to an internet cafe somewhere. There were dozens in Petersburg, for example. The vast majority of them are willing to loan you headsets for a few extra rubles. Then you can talk with your friends back home for a VERY reasonable rate.

Phone cards from landlines are also pretty cheap. I used to use Evroset. It cost 93 kopecks/minute to the US (2 cents or so).