I have a Garmin 800, so I never had much use for my iPhone while riding, except as a phone (they still work like a phone I understand). Then I discovered the Glympse app which with a text to another smartphone, let's someone know where you are (or at least where your phone is). They can follow you on their phone's map for a time period you choose.
I cycle a lot alone, on roads my wife hardly knows. I no longer file a "flight plan" and can even change my mind on the ride and alter my route. If I have problems, my wife can locate me. And when I'm heading back "to the barn", my wife can estimate the time of my arrival, if for no other reason, to get her other fellow out of the house. ;-)
I tried it for a while, then went to Trackme on the Android phone, Cyclemeter on the iPhone. The people I want to keep notified don't use (or don't know how to use) smartphones, so Trackme sends an email with the URL of the map showing my location.