Plantronics wireless phone "PSTN" adapter

[Bear]

Good morning everyone! I have a Plantronics mod# CS55. I want to turn it into a mod# CS55H.
As far as I can tell the only difference is that the CS55H has what is called a "pstn" adapter. It has 3 leads emitting from it. One lead is an RJ11 which plugs into the regular wall phone jack. the second lead is terminated with an RJ22 which plugs into the base unit of said system and the third is terminated with a 3.5mm, 3 conductor mini-plug. I suspect that there is a relay in the adapter. Checking the jack for the 3.mm plug, it would make available either 4.8vdc or 12vdc depending on the use of the tip or ring of the connector and the sleeve. I know that there are a lot of telephone savy people on this board and I was wondering if anybody knows what is, or probably is in this adapter or knows of a circuit I could use.
Why not buy one from Plantronics? They will not sell the adapter itself, but only in conjunction with a new CS55H system. I have found out that re-branded Plantronics adapter is available from NEC for $198 Canadian. Again no information is available. These folks have better security than the U.S. Gov't. This link may help http://plantronics.custhelp.com/cgi-bin ... 1161020336
I did not intend to turn this into a "Doctoral Thesis", but I wanted to give all pertinent information up front and answer all logical questions beforehand.

Thanks for reading.
Take Care

Dennis