I think killer phones would be a lot more interesting back when phones had substance. I find it hard to be threatened by something that fits in the palm of my hand.

Then again, they are making phones larger these days...

oh god it's happening

Relevant.

I think the phones would have better luck at killing us if they were cars.

RoosterTeeth made a trailer for a pretend movie where that is the premise, and Siri goes evil and starts killing people.  Ordinarily I'd link it here, but it's got a touch of swearing and gore, so you'll have to find it on your own.

Also one my argue that this is also the plot of iRobot, Eagle Eye, or any other movie where machines go bad.  Not sure if there's one specifically about evil smart phones, but you can probably expect one to be released soon enough.

What if they could plot to make you miss important calls and prevent you from being able to make calls?

Pretty sure mine already does...

Also the TV show Supernatural had a recent episode about a ghost that traveled through objects that could connect to WiFi which is sort of on that track.

-The number you have reached is trying to kill you.

Hmm, What is with you and telephones?