We have had an issue in the past couple of week with an Fxs port all of a sudden. It is normally a fax line, but when troubleshooting, we realized that you could hear someone on the other end of the line, but they couldnt hear you. It was the same thing on their end. It doesnt matter if we dial internally, or externally through our PRI at another site. When you fax, the other end picks up, but the source end just keeps trying to send the handshake. It is running IOS 12.4 (24) T6. We have changed Fxs cards and moved the slot. We are trying an IOS upgrade now to the 15.1 series. Any thoughts or suggestions?