Quod Libet doesn’t recognize the HTC Desire as a Media Device on Arch Linux. Reason: Quad Libet looks for ‘portable_audio_player’ capability of an USB device. This is controlled by Hal.
The file /usr/share/hal/fdi/information/10freedesktop/10-usb-music-players.fdi contains the definitions of the capabilities. With hal-device, find out the usb.product_id of the HTC Desire:
5: udi = '/org/freedesktop/Hal/devices/usb_device_bb4_ff9_SH07XPL01559_if0' usb.product_id = 4089 (0xff9) (int) usb.vendor = 'High Tech Computer Corp.' (string) usb.product = 'USB Mass Storage Interface' (string)
Add this product_id to the above mentioned file. I found a section for HTC Diamond and added it there:
<match key="@storage.originating_device:usb.product_id" int_outof="0xc01;0xc02;0xc13;0xff9">
Restart hal, plugin the Desire, restart Quod Libet and it should appear in the Media Device pane.