Cellphone cancer study on rats supports the tentative conclusion of the interphone study (with humans): heavy cellphone use increases risk for glioma and a few other selected types of cancer. https://qz.com/1241867/cell-phone-radiation-can-cause-cancer-in-rats-according-to-the-final-results-of-a-us-government-study/ …
I don't think that there is a physical law that says that ionizing radiation is the only way to cause changes in cells that could lead to an increased risk of cancer.