Cellular phones became widely available in Kenya in 2000s but their use has increased dramatically since then.  Currently, 93 percent of Kenyans are mobile phone users. The amount of time that people spend on their phone has also significantly increased.
Research conducted by the American Cancer Society indicate that cell phones produce a form of energy called radio-frequency (RF) waves. Thus there have been questions about  the effects of RF waves to the brain. Lets first get to understand how cellphones (including smartphones) work .
Cell phone work by sending and receiving signals from the nearest  cell towers  using radio-frequency  waves.  RF waves are a form of electromagnetic energy that some researchers have indicated have the ability to break the chemical bonds in DNA. So how is this related to brain cancer or brain tumors?

The radio-frequency  waves from cellular phones come from the antenna of a hand-held Cellular  phone. The RF waves are strongest at the antenna and lose energy as they travel away from the cellular phone.  Typically, the cellular phone is held close to the ear or against the side of the head when making or receiving a call. The closer the antenna is to the head, the greater a caller or receiver is exposed to radio-frequency   energy.  Then again, the body tissues  that are closest to the cellular phone absorb more energy than those that are farther away. So the more time you spend on a call the more energy is absorbed.  The amount of energy that you absorb to your body tissues is called specific absorption rate (SAR).

Cellular phones have different SAR and you should check out to see how much your phone has.  Cellphones that get into Kenya through backdoor  or  fake phones are unregulated thus have their SAR not known. So now you understand the dangers of buying fake phones
Lab studies conducted by scientist have indicated that the effect RF waves have on human cells might possibly help tumors grow. Other scientist have dismissed these results claiming that there is no  correlation between RF waves and tumor growth.

All the above studies are questionable and thus in the meantime as a cellular phone user  it is wise to take early precaution.  Here is where the correlation between whatsapp and brain cancer or brain tumors come in. Use of whatsapp or other messaging services will reduce the said effects of RF waves  have to your head as the cell phone does not come into contact with the head. Therefore consider using  messaging services more for conversing than  calls.
All the scientific studies quoted above are based on  comprehensive data released by the American Cancer Society on Cellphones as a cause of cancer which was Last reviewed on 12/12/2014