If you're talking Google calendar, you don't need an app. Go into your calendar settings on a desktop and set up for mobile use. Then create a contact in your address book with the number 48368. Call the contact "Calendar." Then, using Voice Search or Vlingo or whatever you already use, speak text messages to the contact "calendar". Google calendar will interpret the text and schedule whatever event you want it to on the date and time you tell it to. I did a test recently where I set up an event from 9 to 9:18 a.m. on a certain day, and when I checked my calendar, Google got it perfectly, including the 9:18 stop time for the event. Pretty slick.