Answer:
Although cell phone users abound, most are not well informed about the potential hazards associated with cell phones.
Step-by-step explanation:
In the passage, it can be a transition in sentence 3 because it is presented a situation where people are not well informed about potential hazard which cell phone can make. The transition although explains that there is a fact about many cell phone users, but there are not many pieces of information about the hazard of cell phones.