I believe you are misinformed about the Silica. First, it is not an O/S. Silica is a subset of the CANVAS Pentest suite from Immunity, that has been optimized for wireless pentesting. Also, it is written in python. Not exactly closed source there. Second, silica devices are currently built on the Nokia N810 platform, which has built in GPS. Third, the Nokia N800 series is not closed source either. It is built on osso-linux. My version is running a 2.6.18 kernel.
Originally Posted by relaxis
If you don't want to pay for the custom software, I see Nokia N800 series devices for around $300 - $400 on the interwebs. There are several posts/sites on the web about customizing the device with things like nmap, probably metasploit and other stuff. Haven't checked, but I think that Irongeek may have something on his site about customizing one of these (or similar).
Hope this clears things up a bit.