I think the IVR interface to Bitcoin is a good idea.
If you need a did to continue with your service, I can give you a free shared did, that way your service will be available to everyone from any where in the word at the same time avoiding long distance charges for the calling party. The only problem with shared dids is that the person dialing will need to enter an extension after the number, the good thing is that I can give you one for free, and the calling party saves on long distance.
The shared did you can map it to a phone number (costs money) or to your voip account (free).
Since you use asterisk, you can configure your voip account it your asterisk server.
And since I support IAX2, you can provide the service behind a firewall if you wish without any nat problems.
After you create the account just send me an email, and I will provide you with a shared did free of charge.
to create the account go here http://www.btcvoip.com