The tests involved the creation of "hot zones" in which smartphone users could switch from 3G or 4G service to Wi-Fi. Surprisingly, when the Wi-Fi service was available, the traffic on the cellular network barely moved lower. In some cases, the traffic on the cellular pipeline rose during the test. Deutsche Telekom blames this on the different way smartphone users act in the presence of a Wi-Fi signal. Knowing that using data won't count against their monthly allowance in the face of a Wi-Fi signal is a big factor, leading to the use of more data. Some apps will only fully work over Wi-Fi. If there is no room on the Wi-Fi network, data cannot be offloaded to it from the cellular network.
Some criticized Deutsche Telekom and the study, arguing that the carrier is afraid of losing control over its cellular customers when they are using Wi-Fi. Deutsche Telekom says it will commit to doing further testing. For example, the test that was conducted concentrated on outdoor use of mobile networks, not indoor use where a Wi-Fi signal might be more useful. In addition, the Wi-Fi network was not set as the preferred network for the testing.
Using Wi-Fi to offload cellular traffic can prove a dilemma to carriers. Reducing the amount of traffic on its network can help a mobile operator reduce its cost, but at the same time, getting its customers to use its network more can help the carrier increase the Average Revenue Per User.