I'm not real versed in networking, but a lot of people use the following to "sniff" out open WIFI spots:
1. wellenreiter
2. kismet
You should do a search (In the Sharp/Cacko section) for the above programs.
I haven't used either in a long time, but wellenreiter is more of a GUI type app, where kismet is a console based app.
You may find these programs in *.ipk format for Sharp/Cacko at the link at the top of this forum. "ELSI"