If you still have a home phone line and use an answering machine, one of the things that you probably commonly do is listen in on voice mails as people leave them. That is one of the upsides to a home phone since you can hear what someone has to say and choose to pick up or get back with them later.
Apple has been granted patent by the US Patent and Trademark office that outlines a method of giving iPhone users that same capability. The patent shows a way that Apple could allow iPhone users to listen in on voice mails as they are left.
The patent in question is US Patent No. 8,666,034 and is believed to be an assignment from Rockstar consortium from the purchase of patents Nortel held. The title of the patent is "Audio call screening for hosted voicemail systems."
The Rockstar consortium purchased the patent back in 2011 when it and other firms in the consortium bid $4.5 billion on a cache of over 6000 patents from Nortel. Apple was the backer for $2.6 billion of that purchase amount. The patent shows a method of establishing a conference call connection between the incoming call, voice mail system, and user so the user can listen in real time. The microphone on the listeners phone is left muted or disabled.
SOURCE: Apple Insider