It seems nowadays that just about everyone has a cell phone and that most people use their cell phones a lot, while there are some that even seem to use their cell phone all of the time, no matter what else they may be doing besides just talking, surfing, or texting. The thing is conversations can be distracting, depending upon the attention that you pay to the conversation, and anytime that you look down at your cell phone to read a text, look up a contact, check your facebook, or write a text, you are, by definition, taking your eyes off of something else and that too can be a problem.
The first problem with cell phones is where to place the phone such as, for example, holding it in one of your hands, pretty much no matter whatever else that you're doing, or have it holstered, or have it in a separate spot while using blue tooth for your conversations and texts, or the worst of them all, having your phone in one hand and almost in front of your face, while you are in motion. The thing is that if you are in motion and one of your hands is holding your phone, and if in addition, that phone is blocking one of your eyes or possibly both, your visual motion cues whether you are walking, driving, baby sitting, or whatnot, have been compromised. This means that activities that you would normally be paying vital attention to, such as stairs, sidewalks, lampposts, pedestrians, other drivers, and so forth, are either barely getting the attention necessary to deal with them prudently or being simply placed into a "I got this" zone, when you most definitely do not have it under control.
It's difficult to determine how many car accidents, pedestrian accidents, falls, and so forth, are caused or contributed greatly by the improper usage of cell phones when moving about. The bottom line is most people want to believe that they are always under control when it comes to multi-tasking, and that whatever small distraction that a cell phone might bring to the table, they through their superhuman instincts and razor-sharp reflexes will always have the appropriate counter-response to whatever comes their way.
The thing is that there are two basic problems with this thesis: one is that even ordinary conversations to which your attention is hardly diverted away from what you are currently involved with, can almost without notice, switch over to something that is far more intense, which engages your conscious mind and focal point to such an extent that all other tasks and visual clues are pushed far to the background. Then there is the second problem which is by virtue of having a phone in your hand or in your hand and blocking all or part of your visual field, you are, if walking, placing yourself into a position where your balance can be lost in such a short period of time that to in order to recover from that particular misstep it may be too late to prevent a fall, and now with your valuable cell phone in one hand, you may subconsciously be reluctant to release or slow to release that same valuable phone in order to properly brace your fall. In addition, should you be driving, you may find that road conditions have changed to such an alarming degree, that you need to slam on your brakes, or jerk your steering wheel to maintain your lane, and so forth.
What it comes down to is that using a cell phone is not a free ride that enables you to do all the things that you desire to do without any negative consequences. In fact, there are definitely trade-offs, whether recognized or not, to which negatively impacting your visual field and/or always having one hand gripping a cell phone are not wise choices.