This is an interesting paper. It introduces some work called Soundminer, "a stealthy and context-aware sound Trojan for smartphones".

It explores the threat of smartphone malware with access to on-board sensors, which opens new avenues for secret collection of private information. The trojan intelligently "pulls out" sensitive data such as credit card and PIN numbers from both tone- and speech-based interaction with phone menu systems.

It shows how potential attackers can now target side channel information