I did listen to the entire phone call, several times. Yes, while on the phone Zimmerman stopped chasing the kid. But he knew what direction the kid was heading. When the police suggested meeting up with Zimmerman at the mailboxes, he hesitated and then replied that they should call him so he could give them his exact location. That suggests to me that Zimmerman, after getting off the phone, ran after the kid and caught up with him in someone’s backyard.
A plausible scenario. Although Zimmerman said he didn't know where Martin was, which suggests Martin had a huge head start on Zimmerman. Why wouldn't Martin just run home to his apartment? I would think he would have been safe behind doors long before Zimmerman ever came close. Maybe he was lost? He was only there temporarily maybe in the dark every condo looked the same? I don't have answers.
Zimmerman is the one that mentioned the mailboxes first. After he disengaged the chase with Martin, the 911 dispatcher asked him if he wanted to meet with officers and Zimmerman said yes. The dispatcher asked him where he was going to be and that's when Zimmerman gave him directions to the mailboxes. Actually, he said a past the mailboxes, and that's where his truck is. The dispatcher then asked him what residence he's parked in front of and Zimmerman said he didn't know the address. The dispatcher asked him if he lived in the area, he responded yes, and asked him his apartment number. Zimmerman then said it was a home and started to give the address, stopping short of naming the street, worried that he didn't want to give that information out, probably over the phone.
There is hesitation throughout the call, which is normal for situations like this. I think your imagination is running wild here because there nothing to indicate that Zimmerman was being deceitful or otherwise calculating.