Mobile network takes chargers out of the box to reduce the environmental waste caused by spare and redundant mains adapters for handsets.
O2 phones will not automatically be sold with chargers from 2015.
The mobile network has been trialling selling an HTC smartphone without the USB charger usually supplied with it.
The 'Charger out of the Box' scheme, the first initiative of its kind in the world, offers the HTC One X+ with just a USB-to-micro-USB cable, although customers who need a mains adapter have the option of purchasing one at cost price.
Since the trial began, 82% of customers who bought the handset charger-free did not buy one at a later date.
Ronan Dunne, CEO of O2, said: "The results of the trial demonstrate a clear willingness among consumers to consider and respond to the environmental argument for taking a phone charger-free.
"I hope that as a result of this study the rest of the industry will now consider joining us in our campaign to take chargers out of the box for good."
It's estimated that 30 million new phones are sold in the UK each year, all of which currently have a charger included. If the trial's results were repeated with all handsets, there would be 24 million fewer chargers sold annually in the UK.
Research by O2 suggests there are as many as 100 million unused chargers in total in the UK - either duplicates of existing kit or from old handsets no longer in use.