Don't know about Backtrack (I don't imagine they're going to want to go through and rebuild everything for ARM sources), but you might want to check out the next version of NeoPwn.

The previous version ran on Openmoko, and they announced that the new version is for the N900. I suspect odds are good that they'll get packet injection working.

You can follow it here: http://www.neopwn.com/hardware.php