Probably many know the noise that causes a cell phone if it is within range of a radio. You will then hear a beep and hum of the radio speakers. Now just imagine, it would be no radio nearby and you could hear the same sounds from the phone speaker. Exactly this effect occurred with me (though in a milder form) with two devices on. Both myself (I would have tolerated this) and my interlocutor (since then heard my patience) could be heard in a position they transmit sounds. Unfortunately, the phenomenon did not hang during the conversation, but accompanied each call.
I then Bluetooth and Internet off - both actions had no effect on voice quality.
I need a cell phone for just three things:
1. calls
2. Text messages
3. Alarm Clock
Here are my most important calls. In the café and go the cell phone may fulfill its purpose, but as soon as one is staying in a quiet room, robbed a constant beeping and humming this last nerve.
Because the phone looks simple and elegant, I give two stars. The voice quality did not deserve a single star.
CONCLUSION: Good for casual phone users. But who wants to use the phone for important (eg business) calls and not just staying in the open air (there were no noise on), should be prepared for substandard voice quality.