People this age communicate more by text than through phone calls - the likelihood of a 17 year old male out for a nighttime stroll getting an incoming voice call from a female is low, and the likelihood that he answers the call is even lower.
In that social set, answering a phone when a female who is not your mother calls you makes you seem weak and needy.
The normal sequence is that she sends a text and then he decides whether or not he wants to reply to the text.
Those are all good points.
The thing I find implausible is that she was nearly a witness to the homicide...but once the phone connection was lost, she did absolutely nothing. To me that indicates she most definitely was not on the phone with Martin when the confrontation began.
And if they had been on the phone, wouldn’t the connection have stayed open...complete with her hearing the gunshot?
Now I also doubt he was on a ‘nighttime stroll’ just to enjoy the fresh air. It took him 40 minutes to walk a half mile...this link speculates that he may have bought a ‘blunt’ at the gas station, and spent the 40 minutes enjoying it:
THC was in his blood, confirming his use...and it makes people paranoid, which matches Zimmerman’s initial description of his behavior very well.