Samsung Chrono SCH-R260 User Manual page 215

However, none of the studies can answer questions about long-term
exposures, since the average period of phone use in these studies
was around three years.
What research is needed to decide whether RF exposure
from wireless phones poses a health risk?
A combination of laboratory studies and epidemiological studies of
people actually using wireless phones would provide some of the
data that are needed. Lifetime animal exposure studies could be
completed in a few years.
However, very large numbers of animals would be needed to provide
reliable proof of a cancer promoting effect if one exists.
Epidemiological studies can provide data that is directly applicable to
human populations, but ten or more years' follow-up may be needed
to provide answers about some health effects, such as cancer.
This is because the interval between the time of exposure to a
cancer-causing agent and the time tumors develop - if they do - may
be many, many years. The interpretation of epidemiological studies is
hampered by difficulties in measuring actual RF exposure during day-
to-day use of wireless phones. Many factors affect this
measurement, such as the angle at which the phone is held, or which
model of phone is used.
Health and Safety Information 210