Eric: I don't see any other responses to your request for USB FOB source information, so here is where I got mine: http://www.geeks.com/details.asp?invtid=CL-USCM2&cat=SND The part number/description that was on this site for the units that I purchased was: "CL-SU4CH -- USB 2.0 to Audio Adapter w/Microphone Jack" However, I see they now carry only the CL-USCM2 units. In addition to Jim's warning about the physical difficulty of modifying these FOBs, I would add the comment that the internal sound chip must be the CM-108. I can confirm that the CL-SU4CH contains this chip. I cannot vouch for the CL-USCM2. However, at $6.50 apiece plus shipping, it's not much of a gamble. If I can help you further, feel free to contact me off-list. Good luck! 73, Dave VE7MQ.