Text Box Entry Validation

We have a program that once a user enters a character the cursor jumps to the next entry box, they do not have to press Enter.  For example, we want the learner to type in the character 'H' for Home or 'B' for Business (or 'h' or 'b') for the type of phone number they are about to input.  So as soon as they type in 'H', it immediatly takes them to the number entry box.  But using a text box entry, the learner has to hit the Enter Key for a validation to take place.  Is there a way for the validation to occure after the keystroke?  We've played with the shortcut key, but that will only validate one of the four options...and we need it to validate H, B, h, and b.  Is there a way to do this with Advanced Actions?  Any help is appreciated.  We are using Cp 6.