After getting to the abandoned plant, Amber tries several times to call 911 but cannot get a signal. If a cell phone cannot get a signal to a cell tower to call out, it cannot get a signal to receive a call. So, when Veronica uses Eric's cell to call Ambers, her phone shouldn't have rung as it wouldn't have received a signal.
shareIt probably was a Sprint like my POS, that works when it wants to work, but not when you need it. lol But seriously, I would have agreed with you a few days ago. But while I was changing my cell phone services, I noticed there was an option to block incoming calls, and an option to block outgoing calls. So, that scene may not be totally implausible.
So you're saying she stopped, went into the phone menu and chose "block outgoing calls" to make sure she could never call for help, after they'd just been kidnapped in a truck and then attacked by monsters? Makes total sense! -_-
Actually, after watchng till the end (a tough job, I'll admit) it's not as insane as it would normally seem. It "could" be explained ***SPOILER***
by her having done it subconsciously since it turns out Amber is one of them.