Other mistake: When Casey is in the car boot on the phone to Jordan, Jordan is asking her to describe what she sees in the boot of the car. Casey is naming the items she sees, paint cans, shovel etc. Jordan asks her to pour the paint out of the boot through the tail light hole. Jordan puts out a call to look out for a car with "WHITE paint pouring out the back," but Casey didn't tell her the colour of the paint.
Factual error: In the beginning of the movie, Leah Templeton is killed on Feb 26. Then the newspaper obituary that Jordan had hanging on her locker door says that Leah's service was to be held at 11am on Feb 27. That is not enough time to prepare the body and get her ready for her funeral by 11am the next morning, especially since it's a murder under investigation.
Factual error: The substance he haves her inhale to perform his surgical scalping should be nitrous oxide (laughing gas) not "nitric oxide" which is a substance in our bodies that stimulates vaso-dilation.
Factual error: According to the law in the state of California it is not allowed to smile while the photo for a driving licence is being taken. In the movie the kidnapper is shown with a big smile on his face in the police database. (00:54:39)
Answer: Not if you have absolutely no signal, no, you can't. Mobile phone companies generally have an agreement that any network will carry an emergency call, even if it's not the network that that phone belongs to, so if you were out of range of your own network, another could carry your call, but if you're in a situation where none of the networks can reach you, by definition no calls of any kind can be made.