[Solved]
I am not sure this will work every time, but this is what I found worked for my scenarios and hopefully will allow you to get in the ballpark if you are having the same problems.
Set Deskphone COS
Display Held Call ID on Transfer: Yes <- This is only if you want to send the Original Incoming Caller ID when Transfer the call to another DN.
Set EHDU COS
Hot Desk External User - Display Internal Calling ID: No <- This is only if you want to send the Originating DN's Caller ID instead of its DN to the Cell Phone.
Go to Trunks \ Digital \ ISDN \ ISDN Protocol
Set Enable Unknown TON\NP to Yes
Set Replace External CLID to No
Go to Trunks \ Digital \ ISDN \ Outgoing Call Characteristics \ DID Ranges for CPN Substitution
Setup all of the DID Ranges that will be used from all sources. In my case it was the Local PRI, the Remote PRI, and the SIP Trunks incoming DID Ranges.
Go to Trunks \ Digital \ ISDN \ Outgoing Call Characteristics \ CPN Substitution
Setup the Default Voice & Data CPN as the BTN or Main DID for the company
Add the previous DID Ranges as Members to the CPN Substitution
Now, anytime a call comes from one DN to another and they have an EHDU setup for them the originating DNs Caller ID will be sent out to the EHDU instead of their DN.
Thanks,
TE