Cell phones are just small computers with certain input devices for communication. They remain largely underexploited as mobile environmental sensors with their geolocation attached. Nokia has circulated a concept design (http://www.unwiredview.com/2007/12/10/nokia-eco-sensor-phone-concept/) that would enable just such usage. There's no technological hurdles to the creation of aftermarket sensors that would allow for the monitoring of large amounts of environmental variables. Is there a market for these types of sensors? Possibly not, but they could form the basis for a crowdsourced research project like the measurement of real-time air quality throughout an entire city over a year. The data from such a project could end feeding into projects like MIT's Center for Environmental Sensing and Modeling(http://censam.mit.edu/), which recently launched a pervasive environmental sensing program in Singapore (http://blog.wired.com/wiredscience/2008/01/mit-launches-pe.html).