Your client seems to have shot himself in the foot. If the Cable dialtone company cannot provide Centrex-type features, then they're basically screwed. Short-sighted decisions based on saving a bit oof money can really hurt a company.

There's nothing that you can really do to replace that feature and make it work the way it was before.

I had customers that used the Centrex conference feature, and Centrex transfer outside feature---then switched to a PRI. Those features went away. They just had to learn to live without them.

This might be a time when you can upgrade them to a Partner voicemail card. They would like that situation even better than the original situation. Also, they would save money on the subscription VM. Good Luck.