I am mostly a lurker here but I found that so many people were saying that a stereo headset with a mic would not work (in stereo that is ) through the headphone jack on the top of the x50 (and I assume the x50v is the same).
I do have this working with a $13 dongle purchased from
http://pc-mobile.net/audioadapter.htm. Someone else posted on AximSite this link but I have still seen people posting that it cannot be done.
If you go to the URL I just posted and scroll down to the adapter with the code 'PTAMS' you will see it and a link to the toshiba page where there is more of a description for it.
I have tested it with Skype and with the newest Vonage Softphone Pro for the PPC. They work fine with it as does the Voice Command from Microsoft.
In addition the audio portion comes over both headphone speakers and it sounds the same as if I did not have the adapter.
Now the only caveat is when you order the adapter it is sent from Hong Kong via USPS Air mail (or something) and you have to be home to sign for it (and the shipping is $5). Besides that... it does seem to work fine.
If I notice any problems with it in the future I will post them up.