Just as the title says, is it possible to scan all WiFi access points around the Android phone device when WiFi is turned off (e.g. only using 3G)?
Starting from Android 4.3 JellyBean, it's possible to scan WiFi access points even if the WiFi is off. It's called "Scanning always available"
As those who have taken a spin around the Android 4.3 ROM have noticed, Google has made a change to devices' Wi-Fi settings in Android 4.3.
"To improve location accuracy and for other purposes, Google and other apps may scan for nearby networks, even when Wi-Fi is off," describes Google.
If your device is Android 4.3 or newer, you can enable it from Settings - Wi-Fi - Advanced Wi-Fi - Scanning always available.
Fire up the Settings app and tap your finger on the Wireless and Networks option. Tap on the Wi-Fi option, and then tap on the Overflow button on your phone's screen (the triple-dots icon). When this submenu pops up, tap your finger on the Advanced option. From there, you'll want to make sure to check the "Scanning always available" option if you want to participate in the new Android 4.3 feature. Otherwise, if it's checked, you need merely to uncheck it to ensure that "Wi-Fi off" really means "Wi-Fi off."