It's been done at least a couple of times at MIT: http://people.csail.mit.edu/fadel/wivi/ http://people.csail.mit.edu/fadel/wivi/ http://witrack.csail.mit.edu

It's been done at least a couple of times at MIT: http://people.csail.mit.edu/fadel/wivi/ http://people.csail.mit.edu/fadel/wivi/ http://witrack.csail.mit.edu/ http://witrack.csail.mit.edu/ And at University of Washington: http://wisee.cs.washington.edu/ http://wisee.cs.washington.edu/ And you can check the references of those papers for other sources. Now, whether an app on a smartphone can get enough RF data to do it, is probably an open question, as all of those projects used something custom or other.