If you find the sound quality is not good or there is a large delay, please try the following.

iOS

• Go to "Settings" on the device > Switch on/off "Mobile Data Communication."
• Go to "Settings" on the device > Switch on/off "Wi-Fi."

Android

• Go to "Settings" on the device > "More" > Switch on/off "Mobile Networks."
• Go to "Settings" on the device > Switch on/off "Wi-Fi."

Note: The sound quality depends on the performances of communication line and device both parties use.