In S01E05 of The Wire, why did they need to crack the code the way they did?
Freamon said they got the pages and the numbers of incoming and outgoing calls of the payphones as well as the duration.
Since they still mostly use the phone directly in the low rises and most likely that's one of the phones they get the call information from they could have easily matched the paged callback numbers to any of the (most likely) few phone calls that were made from the payphones in the next minutes.
It kind of feels like they didn't really use these information until they get the wiretap running and actually listen to the conversations.