Okay here's a scenario. DB claims her phone is broken. Let's say that her phone is not restricted because JI's is the main phone and his is restricted but the other one on the plan is not. Because her phone is broken, with speaker/microphone issues, it technically can call but you can't hear on either end of the call. DB knows this so she doesn't bother trying to check her phone to see if it works when the phone is restricted due to lack of payment because there is no sound anyway to check it.
So someone takes the phones and tries to use one of them to call someone. JI's does not work because it's restricted. The phone from the father does not work because it's not connected to the plan yet. DB's phone works but the caller does not hear anything on the other end so assumes it's not working either. The call stays connected for the 50 seconds it takes for the voicemail to disconnect it. If it is an IPhone, just pushing the button to return to the menu does not end the call. Perhaps the call was still going through when someone was checking out other info on the phone.
But whomever it is, they are doing this "very near" to or inside of the Irwin house, over two hours after the couple witnessed a man carrying a baby down the street just around the corner from the Irwin home.
If DB and JI are truly innocent, there has to be some close by neighbours involved in this IMO.