People have noticed a billboard advertising "Non Stop Pop 100.7 FM". It could be an actual station or it could be like GTA III where there were billboards for stations you couldn't listen to. It would fit with the Fergie & Enrique tracks.
It's at about 4:25 of the gameplay trailer, right after the bit with Trevor in the tattoo parlour there's the red car (F620 or SuperGT?) weaving through traffic. The billboard is visible on the right for the first few frames of that shot.