I currently have an on-net 4 digit dial plan deployed in a dispersed TDM environment which is fully utilised. I am transitioning to a unified solution and have determined a five digit plan is the way forward. I have a range of new numbers direct into IPT estate and will migrate from TDM to IPT in a controlled manner. The issue i have is how best to run with a mixed four and five digit dial plan between these two sites. Any specific detail or alternate approaches would be welcome.