Okay, so how about this, Heather didn't respond in the way SM expected her to when he called at 1:35 am. Maybe he was trying to see her and not go back home. She talked with him, didn't want to hear it and blew him off. Then in the time that she called her roommate and got settled in for the night from her date, she thought about and wanted to call him. She eventually called his cell phone, which TM had, hence him using the payphone. TM then told him to answer on the second ring and go along with what she was saying and ask to me at PTL. TM handcuffs SM to the bed, ugh. Then takes off in HIS truck to the landing. From there, whatever happened and she returned and made SM clean his truck and do something with Heather. OMG.
Then there is this, which I think could be likely. He calls Heather, she denies whatever he wants, he returns home, already mad. He returns home and possibly argues with TM about where he has been? Then both M's in bad mood. Heather decides to call him for whatvever reason, no luck with payphone number and then calls his cell. the first call he doesn't answer, telling TM that he doesn't know why Heather would be calling. The next time she calls TM tells him to answer it and coaches him on what to say to get her to come to PTL. They both get in SM truck, TM hiding in the back, Heather is waiting, locks up her car and jumps in, then TM in the back seat, with a gun, a rope, a plastic bag, takes her rage out on Heather, killing her, they drive back to the house and from there, find a way to dispose of body and evidence.