I think you should transfer the call to a speed dial, the speed dial has the mobile number in it.
I think they are using the embedded VM's "2 key to be transferred to the cell phone" option, you are supposed to enter the cell phone number in the mailbox (although speed call will work and MIGHT be preferable in some cases)...
There are a bunch of things that have to be done to set this up, the VM COS needs these options:
Public Network Access via DPNSS- Yes
Public Network to Public Network Connection Allowed-Yes
Non-Verified account codes-Yes
Account Code length-(same as length of VM port extensions)
COR of the VM ports needs to be able to make the call
When entering the cell number I think you need to add the 8/9 or whatever is used for outside access.
There is also potential of issues with what your outbound caller ID is set to (or not set), and if you are passing through CID, and that can very depending on the carrier and type of trunk.
Tracing calls is something a bit more advanced, and the method varies based on the type of trunking, if it's SIP, PRI, or LS Trunks, each has a different method.
I will ask again, has this ever worked? Because there is a bunch of system level things that need to be done before it will work (look in the embedded help could put you on the right track, but I don't remember if there is any reference to this feature in there). Basically, the VM ports need to be able to transfer calls outside the system... sometimes that can be problematic and the "problem" can vary widely.