I switched to an iPhone 5S on T-Mobile from a 4S on Verizon. The sound quality is terrible. It is very tinny and sharp, with almost no bass and too much high frequencies. It also sounds slightly distorted at times. It's so bad that it actually hurts in my ears when I use it with the white Apple headset, so I have to turn the volume way down. I did not have this issue with my 4S on Verizon. Have anyone else experienced this? I don't know if it's the phone or T-Mobile. T-Mobile is supposed to have "HD" sound, but I have not yet called another T-Mobile phone so I don't know if that would make a difference. However, when I call T-Mobile customer service at 611, the sound is just as bad as when I call AT&T or Verizon cell phones or landlines.