This is an Alitigen 5.1 system with all POTS lines. The main extension will ring but when you pick up the calling party can't hear you (you can hear them). This extension only cannot call anyone. You get a dialtone, but you can't dial out. Altiserv shows the unit off-hook when the receiver is lifted but the DTMF tones are not taken by the system (completely ignored). The extension back end is functional as we can check the voicemail etc. We have confirmed that the extension is not on Do Not Disturb or Out Call blocking. I just can't figure what is going on. It's only this one extension on the dial out and transmit voice side. Any ideas anyone? P.S. We have swapped out the telephone handsets with known good units and that isn't the issue. Same problem regardless of handset.