$10

Voices by Josh Clarke (PDF)

The magician and the spectator create a group of random items (either physically or in a list). The spectator is asked to touch one of those items. The magician then gives his/her phone to the spectator to hold. The magician tells his/her phone number to the spectator and asks them to call it with their own phone. The spectator sees their incoming call on the magician's phone and is asked to decline it so their call is sent to voicemail. The spectator turns on their speakerphone and, after the normal greeting, the item they chose is announced at the end of the greeting.

This effect can also be performed with a freely selected playing card. 
This is not an app and it can be done with any phone.

Reviews:

"This trick is very fun to do. The participants are blown away by your ability to be able to predict their chosen item. A big plus with this effect is that the participant uses their own phone to hear the prediction. There are no fancy moves to do and what has to be done is done right in front of your spectator. This is a MUST get effect. Josh has got a winner here!"
Eddie Siller (I.B.M. Ring 356 President, I.B.M. Arizona Territorial Vice President)