I experienced the same behavior when making calls. First, I investigated the cause in an alleged manufacturing defect of the phone, and was already on the verge of it to return; until I was aware of the following fact: I had applied an acquired via Amazon matte screen protector, which should fit exactly on the Lumia 830 as evidenced by the set offer. The film itself was also really great. She only had a significant flaw: When she was properly aligned with reference to the notches at the top of the handset speaker and front camera, they concealed the microphone of the mobile phone (bottom, just below the Windows button), because lacked a hole for it. After removing the film, the voice quality was impeccable.
Moreover, I have nothing to complain about on the device. Previously I had a Samsung Ativ S. The Lumia uses felt a little bit faster, but is broadly comparable. However, the camera is worlds better - that's why I bought also the Lumia 830. And known to be released Nokia, and Microsoft now significantly more likely to OS updates as Samsung. Who before Istallation and operating of Preview for Developers (for uninitiated: The published by Microsoft periodically developer versions of WP, no guarantee, but with me so far without any problems and stable) is not afraid and not so high-quality camera is required, can also mE stay relaxed on the Samsung Ativ S.
