If you are experiencing a problem wherein you can hear a caller, but they can't hear you (or vice-versa) you may be experiencing a NAT issue.

NAT (network address translation) support must be enabled on your handset in most situations.  On the Linksys SPA-942 phones this can be found on the  "Ext X" tab's.

"NAT mapping enable" and "NAT keepalive enable" should both be checked.

In certain situations network issues or security devices (such as firewalls and routers) can cause issues with NAT.  Rebooting your router or firewall appliance can often fix one-way audio problems.

 If you continue to experience once-way audio after checking your phone settings and rebooting your router or firewall, please contact support.