Use encrypted connections (SSL/TLS) such as HTTPS to prevent modification of your Internet traffic by the mobile network operator. Also inspect the SSL certificates you are presented to ensure you are really talking directly to the website you were accessing, not an intermediary.
An alternative is to configure your mobile phone to connect through a Virtual Private Network (VPN), which would encrypt and route your traffic to a computer somewhere else in the world before it goes to its destination, hiding your browsing activity from your service provider, and your location from the websites you visit.
For even more anonymity in web browsing, you may wish to browse over the Tor network. On Android phones, you can do this by installing the Orbot application and the accompanying browser, Orweb.
