i have been researching this all weekend.
i no longer have a land line, but only a cell phone for personal use.
i have a plantronics 655 on a ppc-6700, which picks up background noise (fan, tv, clicking on keyboard like a drum). so i sought out other applications to use other than a simple BT headset.

at first, i thought there has to be someway to use the PDA USB cradle to my PC and use my Logitech wireless headset (i mainly use the headset to play and talk while playing internet games using teamspeak, ventrillo, mumble, etc). there is no mention any where of having telephone conversations be routed from my PDA thru the USB cradle port to my PC so i assume that is not possible.
i then considered the Seido usb cradle since it comes with a audio plug built into the cradle itself and then hook it to my PC sound card. well, i believe the audio plug is "out" only for use of playback of mp3's.

i was about to give up. then it occurred to me... what about installing a bluetooth adapter on my pc? would that enable me to use my logitech wireless headset attached to my pc (which is plugged in via USB) for the use of phone conversations on my PDA? i never found an answer for that. lots of talk of bluetoothing files, keyboard, mice, & printers back and forth from pc <> pda tho.

lastly, at the end of this search, i bumped into the xlink gateway. bluetoothing my PDA to home phone. i have seen a couple posts here and there saying great things. but at a hefty price tag ($129+) compared to a simple bluetooth USB adapter for my pc ($29?).

with the rising use of cell phones / PDA's being the primary communication tool in households, i am surprised there is not a alot of popularity in regards to this.