It was reported before the hearing that the defense was trying to secure time sensitive evidence. The defense went into court ready to seek the cell phone records and acknowledged they had just received discovery. So (IMO) when they stated the phone was discontinued the next day, they already had that info.
Yes, but the boys had the phone so I am not sure what the mystery is. They would quickly have learned it was not working if they tried to call the owner or her employer.
They may have learned it was not working simply by turning it on if it was a prepaid type phone.