Snips is a open source offline voice recognition platform that runs on Android and Linux and can be deployed on a Raspberry Pi.
Last years Chaos Computer Club Congress in Berlin already had a talk about this topic. This year, GSM eavesdropping has actually been demonstrated using a cheap of the shelf Motorola phone with an open source GSM firmware as a listening device. Karsten Nohl and Sylvain Munaut replaced the firmware on the phone, enabling them to process all the data it received. They used already available 2 Terrabytes of rainbow tables to decrypt data being sent to and from other mobile phones. They have no plans to release the hack publicly, however they expect others to successfully attempt the hack. Mr. Nohl said the objective was to raise awareness of GSM insecurity. Yikes!