A lot of people would ignore a 3am phone call.
A lot of people 'sleeping like a log' would not hear it.
A lot of people with answering machines would let it do it's job.
A lot of people would not get to the phone before the answering machine clicked in.
In my opinion and experience MOST people would answer a phonecall at 3am for the simple reason that it is an unusual time for a call and could be an emergency.
"Sleeping like a log" is just an expression and sleep varies from person to person. None of us know if Jeremy was easily awoken. It is a waste of time pondering this!
I don´t think a lot of people would let an answering machine do its job when the phone rings at 3am, same reason as the first paragraph. Besides, we don´t know whether Jeremy had turned off his answering machine, whether it was full or whatever. You cannot prove anything by this.
You don´t know how Jeremy´s answering machine operated. You don´t know whether it was on or off.