If it supports H.323, you will probably find it cheaper to use your ATA with DUAL Talk. Configuration details for the ATA are shown at dualtalk.com/ata186config.htx.
I have the same problems us yours. I have dial tone when I pick up the handset, but when I finished the dialing and hear busy tone. I need configuration page for CISCO ATA 186
Just had some $e}{ with ATA and N2P last week. Got it working…as I hope. Can you describe problem more detailed? Also, using cisco debug tool pserv.exe gives you more information about dialing process.This helps you solve problem…If you want, write me email to (russian-bear at mail dot ru) and we will try to get your ATA working.