Cell phones on the field.
 

I'm pretty old school, but had two incidents in summer ball last year that are making me change my mind. One, an assistant coach took a line drive just above his eye. KO, split forehead, much blood. Incredible, but his (adult) team dragged him to the bench and said "play on!" refusing help for him. We prevailed on a passerby to get 911 and had him transported. Later that week at another game an outfielder had a seizure during warm ups...no one had a phone. He dropped as we were taking the field...very scary. Both situations seem like big liability issues for us, the umpires.

So I think in those games that lack league/school representation, i.e. summer ball, I'm going to stick my phone in my back pocket

I too thought about keeping a phone on the field just in case of emergency. I contemplated buying a pay by the minute phone i.e.; Trackphone. It would be small enough to keep in my left ball bag or pocket. I could program in local emergency numbers just in case I had a medical problem or an out of control fan that needed police persuasion. No one would have the number, so I would not get calls. Actually, I would just leave it off. I haven't done this yet, but I do like the idea of being prepared (life long scout here).