I'm pretty sure MetroPCS enables Data Maximizer by default, T-Mobile definitely has Data Maximizer on automatically.
Metro link, then click to learn more about Data Maximizer:
Data Maximizer works by automatically streaming video at resolutions that are ideal for smartphone screens. This technology allows you to
watch DVD quality video and stream up to 3X longer. Without Data Maximizer, streaming video unnecessarily draws previous high-speed data at extremely fast rates, forcing you to reach your data limits early and slowing you down. Now, you are able to reserve your high speed data for the things like surfing the web, social networking, and downloading music or games.
Should you not want to include the feature on your plan, you may simply turn it off at any time.