I'm curious, in that setup, are you paying this third party, the one who imported your real DID, for inbound mins? or a flat monthly fee for inbound calling?
Its a flat monthly fee I believe, all rolled into one bill. So breaking out the phone part may be tough. I am going to dig into the "Did we "Really" need to port our DID. For now, it is so convoluted and fraught with WTF's, I am going to suggest that we go ahead and rather we can or cannot, just add the warning. Easy peasy.
Well, if you didn't run the call through them, you'd need a way to send the CID information to that vendor so they could give you the screen pops to the ERP for your call center. I'm guessing you could have an function on the PBX that makes an API call to the vendor, definitely would be the cleaner way to do it... you also get to control your inbound costs.
I also wonder if the current solution allows them to be in the call path for voice recording purposes? I don't understand the RTP stuff enough to know. i.e. could that vendor be eavesdropping on all of your calls?