Set up ATA ext. to dial ext 21 when going off hook. This is so this ext. can integrate with a Viking E-50 door phone and C-1000-A controller. Even though the ATA ext. is doing its thing when going off hook, when you push button on E-50 it does not handshake with ATA and ring ext.21. Has anyone out there ever had this configuration with a Viking and Norstar product.