APPLE INSIDER
T-Mobile plans to enroll its wireless subscribers — including iPhone users — automatically into a program that will use their online activity to target ads. Here’s how to opt out of the “feature.”

The new privacy policy, which takes effect on April 26, reportedly gives T-Mobile permission to sell your online activity from their mobile networks to ad partners on the network. This can include data from mobile apps or web browsers.
Source: APPLE INSIDER