In 2013, Opera introduced a new service called "Opera Max", which is an app that is targeted towards those who use limited data plans. The app basically uses a Virtual Private Network(VPN) that measures the data usage on your phone. After the app is installed and enabled, all the non-encrypted data requests are sent through Opera's compression servers that optimize video, images and websites and compress them to use less data. They then measure how much data you use and how much you saved.
The service, in 2013, was open only for beta testers. However, now, in 2014, the service is officially available on the Google Playstore for download.
The app is currently in it's beta stage and requires Android 4.0 and above on your Android smartphone. There is no iOS version so far.