That's not how it works.
The electromagnetic waves from mobile phones do not cause the initial mutation that causes a cell to turn into a cancer cell and multiply out of control. That fact has been long established and is not contested here.
What microwaves in the frequency ranges used by cell phones have been shown to do is to promote the growth of existing cancel cells.
Mutations into cancer cells are actually not as uncommon as most people think. All of us have had cancer cells many many times, but what normally happens is that the immune system detects the microtumour and kills it long before it has grown large enough to cause a serious problem.
All of us have been exposed to cosmic radiation, practically all of us have had X-rays a few times in our lives, all of us have inhaled and ingested carcinogenic chemicals from car exhaust, pollution, first- or second-hand tobacco smoke etc. etc.
Carcinogens are all around us, but you don't get cancer that easily.
Cancer risk is about probabilities: many different factors are at play.
And radio frequencies in the part of the microwave spectrum, at frequencies and levels that mobile phones use - have been proven in several studies (I have heard of two beside the California study) to be one of those factors.