If so he was never going to come forward, was he? Therefore they will never know who took part in that phone call, they will be left with just with the suspicion that one of them was CB.
There's very limited investigation avenues available on a solitary phone call.
If it's a burner and it's looking like it is, once you have the number, traced it and requested the network provider to provide a log of all calls / messages in or out, and then tried to find it's purchase point, you're at a dead end (bearing in mind the time lag).
What I would say, is that if that phone had either very limited use or only one use, then that's deeply suspicious and evidence in itself. But the chances of a nefarious character voluntarily popping by and telling the police they were the other party they are looking for is......it's not happening.
Having said all that, if one party in this alleged call is savvy enough to use a burner, but then CB, the career criminal / sex case isn't, then that's not scanning at all. They'd both be on burners if they're planning a kidnapping.