Calltag is an app that's like a cross between hashtags and caller identification. The app by United Minds is designed so that when you use the app, you're able to send tags to another user so that they get some context about what the call will be about.
For example, through iMessage, you're able to include tags like #important and #work before making a call through Calltag. On the other end, someone who is receiving a call is better equipped with information and doesn't need to waste their time on a call that's unwanted.
Serving as a cross that's somewhere in between calling and text messaging, currently, the Calltag app works on iPhone, iPad and iPod devices and can be downloaded for free.