Cellphones already do, or will likely soon be required to, carry location information. In fact, location info of cellphones is going to be the backbone of Enhanced 911.
Now, utilizing the phones as environmental sensors sounds quite intriguing. Of course, one is not likely to stick the phone in a mud-swamp and walk away, so they are going to be useful only as very ephemeral sensors.
There is a use for [Streaming Databases] typically in AVL (automated vehicle location) applications when one is tracking moving vehicles, and typically is going to throw away the historical trace. I haven't seen it yet. I have worked on an AVL application, and that jerry-rigged a streaming solution out of an rdbms.
Intersystems Caché database was used in building an interesting application fir collecting data points streaming from cameras mounted on the helmets of ice-hockey players. Pretty interesting stuff.