The new feature was discovered by Apple Insider through the iPhone's system options when running iOS 6.
According to the menu, the Wi-Fi plus cellular option "allows apps having trouble with Wi-Fi to use cellular data."
This will enable the iOS device to revert to using its 3G connection when faced with a weak Wi-Fi network to maintain fast wireless speeds. Currently, iOS devices will remain connected to weak Wi-Fi signals in place of 3G data, unless the user manually turns off the Wi-Fi option or forces the device to "forget" the Wi-Fi network.
Apple will launch iOS 6 with the new iPhone, which is said to have a smaller 19-pin connector rather than the current model's 30-pin port, along with the wider 16x9 screen in a longer form factor.
Supposed images of the new iPhone were leaked online last week.
The new operating system will no longer include a pre-loaded YouTube app due to a license expiration between Apple and Google. Google will instead release its own Youtube app through the Apple app store.
Apple is expected to announce the new iPhone during a special event on September 12. Rumors currently suggest that it will then launch later in September.