You can add contact shortcut to Home screen on Galaxy S3 with the default 1x1 Android widget size. You just need to tap the contact shortcut and numbers for that contact is shown immediately. Follow the instruction:
1. Open "Contacts" app
2. Tap the contact to open the contact's details
3. Press menu button and tap "Add shortcut to home"
** You may need to scroll down to find this option
4. The shortcut for that contact created
Note that this Android widget is availabe on almost every Samsung Galaxy devices with Gingerbread, ICS, or Jelly Bean