I think we are being played. I think, if this wasn't a land line number, Lori left her cellphone behind when she set off for her new life in Idaho, and didn't want to be located. I really don't think she wanted anyone to know where she'd gone when she lied to the old school about where she was going, didn't transfer JJ's school records to his new temporary school, ran away from Charles' death investigation, and was planning on killing her children (IMO). If she left it behind, she probably gave it to Alex to use when he was in AZ, as a decoy phone, so that he couldn't be located by his phone in AZ during the shooting, but he had it to use wherever he slept the night before.
moo