If you have a situation where you cannot hear people for both incoming and/or outgoing calls and they cannot hear you then please run a traceroute on your PC by following the instructions here.
Please send over the results to us so that we can advise further. Issues such as this tend to be network related.
Another test you can do is the 'Echo Test' by dialling *43 on your Dialler to see if you can hear back your own voice?
Please try rebooting the router as if network this may resolve the issue.
If you can please contact us and advise what make and model of router you are using and who your broadband provider is.