Messages can be filtered using the area at the top of the History List workspace.

Consider the example below.  The soft keyboard will immediately display as the filter field is selected.

The History List will immediately start to filter as characters are typed.

The filtering is case-independent.

Note the "X" and "Cancel" buttons that also then appear to the right.

    •  This appears on both iOS and Android devices but the operation is subtly different:
      • On iOS:  This clears the filter text but leaves the keyboard on-screen
      • On Android: This clears the filter text AND hides the on-screen keyboard

    •   This appears on iOS only and hides the on-screen keyboard.