The reason why they wanted the person who phoned that number to come forward was to tell them who he or she was talking to. That means they can't prove beyond reasonable doubt that the phone belonged to Brueckner.
Even if it was Brueckner's phone the data they have places it within the area covered by the Vodaphone mast in PdL between 7.30 and 8pm. It doesn't place him near apartment 5A. It doesn't place him in the vicinity when Madeleine McCann disappeared, whatever time that happened.
I think you are placing more importance on the phone data in this case than it actually has.
I don't disagree that finding the other caller could allow BKA to elimate any doubt that he was the person taking the call. It's a very obvious move that the Prosecutor would take in order to strengthen their case.
But the discussion was about where the onus of proof lies in relation to phone data. In a court of law, mobile phone data is seen as compelling evidence. Because it is obvious that 99% of the time, the person using a phone is the person who owns the phone. So, my point remains. If BKA can prove the phone belongs to him, and CB wants to claim he wasn't in PDL, the onus will still fall on CB to give the Judge a credible reason for his phone being there without him, else the court will assume the phone was indeed with him.