Yea. Throw out your panasonic pbx and swtich to Asterisk. I just did and its going to save me about â‚¬5000 this year!
What you want to do will only work, efficiently, if your Panasonic PBX uses ISDN.
Very simply, you will be putting an Asterisk server between your Panasonic PBX and the outside world.
You will then program the Asterisk server to call your Panasonic PBX with different "Called Party Number"s depending on the callers selections in the IVR. You then program your Panasonic PBX to forward these calls to a particular extension or ring group. Same way as you would set it up for DID numbers.
I suspect you will find it cheaper to buy a voice announcer card for your Panasonic PBX, unless you already have some equipment.