On Wednesday, another study was added to the list.
A European study involving nearly 1,000 participants found no link between cell phone use and brain tumors in children and adolescents.
The study, published in the Journal of the National Cancer Institute, was prompted by concerns that this age group might have been particularly sensitive to phone emissions. But two decades of research indicated that not to be the case.
The latest study "shows that a large and immediate risk of cell phones causing brain tumors in children can be excluded," said Martin Roosli, lead author of the study and an epidemiologist at the Swiss Tropical and Public Health Institute in Basel.
The announcement comes on the heels of three other high-profile studies, with two coming this month, and one just weeks prior.
A study carried out for the Institute of Cancer Research found "no convincing evidence of a link" between the technology and brain tumors, on July 2.
That review, done by a committee of experts from Britain, the United States and Sweden, concluded there was no risk. It also found a lack of established biological mechanisms by which radio signals from mobile phones might trigger tumors.
"Although there remains some uncertainty, the trend in the accumulating evidence is increasingly against the hypothesis that mobile phone use can cause brain tumors in adults," researchers said.
Sounds definitive enough. But another study, carrying its own authority and released on the same day, says cell phones and brains don't mix.
A Swedish study found large increased incidence of astrocytoma, the most common form of a malignant brain tumor, in those who had been using cell phones for over 10 years.
Published in the International Journal of Oncology, and carried out by researchers from the University Hospital of Örebro and Umeå University (Sweden), the study found that long-term usage increased the risk of all malignant tumors by 30 percent, and astrocytomas in particular by 40 percent.
The studies come just two months after the World Health Organization's (WHO) International Agency for Research on Cancer (IARC) decided cellphone use should be classified as "possibly carcinogenic to humans."
With evidence mounting on both sides of the issue, it's difficult to make a definite conclusion. To play it safe, some users have adopted hands-free sets to keep a distance between their devices and their heads.
There are currently 5 billion devices in use globally.