Would vampires be able to use smartphones?
The touch screens work by conducting electricity in your fingertips to know where you are touching and this works to reduce butt dialing. Would undead flesh still carry the necessary electrical charge to activate the sensors on the screen?
And can you imagine the horror?
Think of a beautiful, vain socialite who decides to become a vampire to achieve eternal youth. She goes through with it. In her glee on waking up the first night she goes to gloat online, only to discover that her smartphone won't respond to her touch!
Cue the screaming.