AndrewWTI thanks for the input. I might go that route. I'll PM you if I need one. I just did a search on the Plantronics web site for compatibility with the CS50 and Partner 18D and it was not compatible.
I have used the CS50 w/HL10 on a Partner 18D before and it worked like a charm.
The point I was trying to make on my previous post is I don't believe the compatibility results from Plantronics. Point proven again. Thanks!