The DAHDIGroup won't show as connected because it isn't a trunk. Perhaps we should update the code to show n/a in the status. I will put it on the list.
If inbound callers are getting busy tones it is likely that your Asterisk setup is not recognizing far-end disconnect correctly. You should speak to your Digium supplier about the correct set-up for disconnect detection on AT&T lines.
Kind Regards
S