Question about WiFi calling/routers for the tech savvy

Hey guys,

So in "Scream 4," Sidney and Kirby have a conversation about calling 911.

Kirby: I tried calling 911 but the land line's dead and someone smashed the router.

Sidney: It's ok, I think I got through on my cell.

Am I wrong in assuming the router Kirby's talking about has something to do with cellular phone service? I thought at first she meant internet but then realized that doesn't make sense in the context of the above conversation. Assuming she's talking about cell service, this is related to WiFi calling which I don't know much about. I've done some reading on it but I still don't really get it. First of all, Kirby has an iPhone which I didn't think had this WiFi calling service to begin with. Second, she receives a call on her iPhone minutes later. How does any of these work together to make a logical explanation for what she said and later being able to receive the call? And wouldn't she be able to use her service provider's signal instead of the WiFi connection regardless to call for help?

Sorry if that was circular and made no sense, I just don't get it. And yes, I know it's a movie, I just want to know if any of this could be summed up in a way that accounts for all the details and still makes sense. If you know anything about WiFi calling (or VMA calling or whatever), feel free to give input.

Edited July 14, 201114 yr by alexisfan07