I completely agree. I can't make it make sense, otherwise. I think the payphone call to Heather was legitimate, on SM's part. I imagine the sexcapades being fueled by alcohol, and SM doing what he always does - humoring TM to avoid a huge fight. Only, an eventual fight happened between them, anyway. With TM passed out at home, SM couldn't access his phone, without the code, so he left her there, and went to the payphone to call Heather. It was cold that night, by MB standards, so he didn't just sit at the payphone, after Heather dismissed his claims of leaving TM. He went back home. Heather couldn't get it out of her head, so she called the payphone back. SM wasn't there, so she called his cell. By that time, he may have also been sleeping it off. The second call to his phone (or maybe even the first) woke up TM & SM and one of them answered. After that???
JMO and stuff.
ETA: I just read a scenario, where the fight ensued after the Broadway at the Beach IE, and TM kicked SM out of the truck, explaining why he chose a payphone at 10th Ave N. This also makes total sense. Dangit. Just when I think I have something, I end up with something slightly or even completely different every time.