If the BIOS (or some commonly used FPGA) already have builtin some kind of backdoor could be used for this. Now, if it was over a hardware backdoor in so many models it should be pretty widespread.

http://blog.erratasec.com/2012/05/bogus-story-no-chinese-bac... http://news.softpedia.com/news/Secret-3G-Radio-in-Every-Inte...