If neither party can hear each other on the phone when making or receiving calls this could be down to the following reasons:
1. Please make sure that SIP ALG has been disabled on your router - this can block VoIP packets of data and so can affect VoIP traffic resulting in call quality being affected in this way.
2. Please make sure that your firewall is not blocking the audio ports for the VoIP call. The real time transport protocol (RTP) uses ports 10,000 through 20,000 so these will need to be open on the firewall to allow VoIP packets to be passed over the network.
Please contact our Support Helpdesk if after doing the above there is still an issue on the line so that we can investigate further.