Hi Cheelo,

1) I am not aware much of the first argument, however have found
this:
   http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=3014032&SiteID=1

2) yes, i have the same experience, dwTxDevice affects audio device
only;

Indexes of devices can be found in ril.h:
#define RIL_AUDIO_NONE
(0x00000000)      // No audio devices
#define RIL_AUDIO_HANDSET                         (0x00000001)      //
Handset
#define RIL_AUDIO_SPEAKERPHONE             (0x00000002)      //
Speakerphone
#define RIL_AUDIO_HEADSET                         (0x00000003)      //
Headset
#define RIL_AUDIO_CARKIT
(0x00000004)      // Carkit
however MSDN says only 0 and 1 are supported values:
http://msdn.microsoft.com/en-us/library/aa919626.aspx

I used these values only, and confirm RIL_SetAudioDevices works as
expected;
To enable speakerphone RIL_AUDIO_NONE should be passed,
and to enable earpiece - RIL_AUDIO_HANDSET;

There is still way to know about hardware, with use of
RIL_GetAudioDevices():
http://msdn.microsoft.com/en-us/library/aa919176.aspx

However i cannot say if it fails or works properly;

Best regards,
Dmitry