If you have dialtonedetect set to Yes, then dial delay will do nothing. When the tenor receives a call from IP, it will route it to the first available pstn line (based on your hunt setting). It will go off-hook on the line and try to detect a standard dialtone. If it cannot detect this, then the call will be disconnected. You can try to disable dialtonedetect and set dialdelay for 500 (500ms) and see if that helps.