bluetooth headset info quest

[Carl Karsten]

I am on a quest for knowledge: I want to understand why all bluethooth devices 
don't work with all bluetooth devices.  I kinda get that there are “profiles” 
which seem to be another word for protocol.  I have also heard that the current 
version of Mac OSC (4A428 ?) doesn't support the bluetooth headset profile, but 
the next version of the OS will.  That suggests that profile support is a software 
thing.

I have applications of this knowledge:
1)a friend says: : I need to know if i can connect a bluetooth audio handset to a 
fujitsu siemens 420 aka hp iPAQ 4150.  I am guessing no,  because pdf Page 80 
(printed 8-4) does not list "headset" 
http://h200001.www2.hp.com/bc/docs/support/SupportManual/c00046424/c00046424.pdf

2)I have a toshiba 6100 laptop that did not come with bluetooth.  For $60 I can 
get the internal addon, or $25 I can get various usb or pccard things.  But not 
all the $25 options list the headset profile, so once again, is the limitation 
hardware, firmware, software, marketing-ware, vapor-ware, new-wave-ware, or what?! 
  And is the $60 internal bluetooth thing going to work with Linux, or is it some 
super secrit thing like the built in CF card reader that doesn't even show up 
under lsusb, but I am pretty sure it uses the usb bus.

I have read about 30 google hits, and the best info was in this list's archives. 
So I figure I will get some straight answers here.

Carl Karsten