We run 6.1(2). When a phone transfers a call to the PSTN (via MGCP controlled gateway), the CLID on the PSTN device (for example, a cell phone) displays from the phone that transferred - NOT the original calling party.
The application, here, in particular is for Mobilitiy (SNR). When our operator answers the call and then transfers it to the employee, both their desk and cell phone ring; while the caller-id on the desk phone shows the original calling party, the cell phone shows the outpulsed digits from the operator's phone.
I noticed the same behavior, though, when simply transferring calls.
If I call voip phone 1 to voip phone 2, then transfer from 2 to the PSTN cell phone, the caller-id on the cell phone is the outpulsed digits from voip phone 2, not voip phone 1.
The transfer is done via (a) transfer, (b) dial numbers then (c) immediately press transfer to release the call.