Let's take a little look at the current Radio Dial in New York, not including Pirate Stations, here are the categories that get covered...
Russian, Jazz, Freeform, Variety/Educational, Rock, Spanish, Caribbean Music, News/Talk/Public Affairs, Religious, Pop, Classical Music, Urban, Rhythmic (Dance), Adult Contemporary and Classic Rock.
Since Rockstar are going to get a lot more real on things they will obviously look at whats on the airwaves, many of the mags have said that what will be played isn't all going to be modern, well looking at modern day NYC radio, Classical, Classic Rock and Adult Contemporary covers that easy. That eastern European dance station that was confirmed, could easily pass off for the Russian and Dance station in NYC. We know there will be a talk station, always will be at least one. We can cut Educational off the list, doubt something like that would appear in GTA, plus if it were, it would be merged with Talk, same goes for Religion. If they are basing it off this charter, we can roughly assume the choice of stations in GTA4.