Crowtalks,
Sorry I have been very busy today and haven't been on the forums, but yes you can put any extension as a DSS/BLF on a phone, but if you want to get a call either holding or ringing you need to use the reverse transfer code (default: 4) first before pressing the key; that part may have been a little unclear in my first response.
As for Dwayneg's solution it will work if the Phantom Extension is in the ring group and it will flash the phone as they suggest, but the catch-22 is that if more than one person presses the secondary key to answer the phone two of them may end up talking to one another.
Explanation: Let's say a call comes into the hunt group and all members are busy so the only phone ringing would be the phantom port. Now let's say that 3 non-hunt group members, lets call them a user, presses the flashing secondary extension key at approximately the same time to try and service the call. What happens is one of those users will answer the actual call waiting in the hunt group and everything works as planned. Another of the users at that point will actually be calling the phantom extension because it works just like any other DSS/BLF and the third user then answers the call ringing the phantom port; hence they are talking to one another.
Now, I am not saying the solution is a bad one, as I have used it several times, but you need to let the users know about that scenario (issue) and that the system is working as designed and that there is not a fix for the problem of the users talking to one another.
Thanks,
TE