Hi,
Running FreePBX 2.11.0.37 with Asterisk Ver. 11.8.1 and we are getting random dropped calls on our FXO trunks.
This has happened using both a card from Rhino Equipment and is now happening with a Digium card.
Length of call has varied on dropped calls. Doesn’t happen everyday.
Anyone have any clues?
Thanks,
Westley
Does it happen more often when it rains?
A PBX is much more sensitive to line voltage that a traditional phone or key system.
If you get more drops on a damp day you have a bad feeder cable or splice.
If you have invested in 2 different cards I would call your provider.
ATT says our lines are clean. 
Other thinks to check would include call waiting service on the line, a bad thing, and false triggering of any busy detect you might have set up, unnecessary on AT&T PSTN lines.
Log dates and times then look at the asterisk logs. I did commercial installs and worked on the hardware side and I can say 98% of the time it is the carrier.
Good example: last week got a email that phones are down and carrier confirms everything is fine. I log in and see the trunk is fubar. Told them what to tell the telco and to escalate til someone does something. 30 minutes later telco confirms a power issue at the mdf. Confirm your wiring from the dmark then ride wm like a small horse. Also make sure you dont have callprogress or busydetect set.