Configuring a FAX or an Analog Phone on port 2 of an ATA 188 drops the call - the phone or FAX will ring but the call gets dropped once it is picked up. Other ATA's are setup the same way just not sure if it is a Calling Search Space issue or not, but have checked all configs for identical setups and they are the same.
This is a known issue when using SCCP. By default the first port uses G729 and the second port uses G711 so you need to confirm your regions are set up correctly or you have a transcoder on the CCM if port 2 is registered properly.
Check the bug: CSCdy55472: 2nd port not doing g729, when 1st port idle, SCCP