The info you find here it's just basically the rates, and that's updated. Talking about how to buy and how to set-up it's a bit more complicated and it changes from country to country. Surely a direct experience is the most helpful thing.
BTW if you are interested in data settings for MT:S, take a look here:
http://www.mts.telekom.yu/index.php?ID=22404 (for 3G)
http://www.mts.telekom.yu/index.php?ID=22450 (for GPRS)
Here it's for VIP:
http://konfiguracija.vipmobile.co.yu/
And here it's for Telenor:
http://www.telenor.co.yu/?section=private&page=258
No idea about documents needed and so on, but usually in eastern countries no registration is required. BTW just ask the seller.