If Stumbler Plus is crashing on your 3.0 firmware of the iPhone or iPhone touch then I would suggest the following:
1. Install Stumbler Plus, wget, and openSSH via Cydia
2. Restart the device by holding down the power button and choosing shutdown then power up again
3. Connect to a wireless network and get the IP (Settings -> Wi-Fi -> click circled blue right arrow for more details)
4. With an SSH client (putty or command line ssh) connect to the device IP. Accept the certificate. Login with "root" as the user and "alpine" as the password
5. Type the following:
wget http://www.iphone.mysticwall.com/download/StumblerPlus-1.2rev1.tar.gz
tar -xf StumblerPlus-1.2rev1.tar.gz
cp -vfr StumblerPlus.app /private/var/stash/Applications.pwn/
rm -vfr StumblerPlus.app
6. You can now launch Stumbler Plus
