Video streaming is probably the highest data consuming activity for most people. Audio streaming comes in second. According to AT&T’s online data calculator, 30 hours of music a month would consume 850 MB of internet. While video streaming in standard definition for 10 hours will consume around 2.44 GB data, the same in HD will use 8.47 GB. Netflix recommends a 3 mbps line for SD quality streaming.
Some carriers like T-mobile provides free data for Netflix and Pandora where the user is not charged for the data used on these apps from their network.
Source: NY Times