I am installing a new hx5000 to replace my customers inter tel axxess system. I was able to do a conversion on the database and get it loaded into the 5000. We are reusing 95 of their current model phones 8520 and standard digital terminal part# 550.4400. I plugged both model phones into the 5000 and couldn't get them to come up. I know they work on the second pair and I tried reversing polarity. We did sell them some new mitel 8528 phones that will work on the ports that I tried to get the inter tel phones to work on. Is there something in programming I need to force them to work? Or are the inter tel phones not compatible?