In the good old days before mobiles, you noted the phone number when you were at someone's home, and then called it hoping that person would pick up. If someone else picked it up, you hung up quickly. Or if you're sneaky, keep talking pretending you called the wrong number. Try to find out who's living with him
If Keli actually had a mobile with her at the hospital, and the police investigation was not aware of it, that's one big gaping hole

if she didn't tell then, why should she tell Hayley now?
If Andrew didn't have a mobile then (or not giving number to Keli, remember that was not a common thing to do because mobile calls were "expensive'), he and Mel did have to wait all morning at home on that Saturday morning, to pick up her phone call