Hi, My name is Eric Moyers. I am a Network Support Engineer in the Cisco Small Business Support Center.
Our devices emulate a standard PSTN set up. If that is working for you, as in this case, based your circumstances, I would change the ‘reorder delay’ (regional tab, control timer values(sec) heading, reorder delay), default is 5, change that to 255. This change should allow the phones to automatically go on hook instead of hearing the busy signal.
Please let me know if this helps.
Eric Moyers
Cisco Network Support Engineer
1-866-606-1866