It all depends on what you want to do.
You can setup your a400 to snd or rcv calls to/from cms and I would assume the same is true for the voip phone. However, keep in mind that the CMS does not do ip-to-ip calls directly. If you want to do that, you would need to use 2 t1 ports to create a loop connection so the call comes from IP to the cms out t1-1, in on t1-2 and out to ip to your voip phone. Not really the best way to do this.