Karl:
Is the call quality poor/static on internal calls as well as external? If it is the issue may not be with the FXO.
To assist in troubleshooting make a call from one of the affected phones to an internal line, then another to an external line (be sure not to use a desitnation inside the building - cell phone, analog line, etc.) Call off-premise to a known clear line. If the internal call has static the source may be in your physical location. If the external call has static it may be in the FXO or PSTN. If both have static then you need to troubleshoot from either end to the middle.
If only a few calls are impacted, say one of every X calls, perform a few call traces from the bad calls. Take a maintenance window and shut some of the FXO interfaces that did not show up on the bad traces, allowing you to possibly isolate a bad line.
Make adjustments to your environment one at a time (input gain, output attenuation, ...) and test between. Check your cabling to prevent electrical induction with sources in-house. Check grounding for the analog line connections at the demarcation point.
One issue we were troubleshooting for weeks was intermittent static on various phones. It ended up being a cell phone using TDMA through the service provider. Close proximity to a IP phone or the router FXO produced static when the (cell) phone was on a call, ringing, or sending keep-alives to the tower every 30 seconds. Cell phones using IDEN (Nextel's legacy wireless) were also found to interfere with IP phone calls - these include Blackberry devices. The cell phones don't even need to be involved in the call, just located close to a IP phone when that call is made.
Hope that helps out.
Tom
