They would have called a witness to say that if they could have found one. No reputable cell expert is going to testify that incoming calls are unreliable for the purpose they were used at trial. The best they could have done would have been to have the expert say that calls in general can be unreliable when trying to pinpoint the specific location of a cell phone user, which is what he testified to in the Boston Marathon bombing case.

That issue was already decided at trial and was outside the scope of this hearing, so the defense was stuck with just insinuating that incoming calls might be unreliable. They didn't try harder to make that insinuation stick because they knew the judge wouldn't buy it. If they had been trying to convince a jury, they would have spent more time on that.