Is the call quality good?

In most cases, when you launch a call from the Onoff application, your SIM card takes over to make the call, so there's no loss of quality - it all depends on your GSM network.

When you receive a call, by default, the application suggests you take the call using the Internet network: this is called a VoIP (Voice over IP) call. Depending on the state and quality of your 3G/4G network or Wi-Fi connection, you may experience differences in call quality.