Hi, Chris.
I've provided the solution, that would give the OP such functionality.
set the value property of the textbox to be initialised with that value i think . .
I don't think it's more handy approach. Because:
1. You have to show/hide/replace mask along user inputs text.
2. You still need to take control over user input (to validate the users input).
We have such a good control, MaskedTextBox. Yes, it's not almighty, so we sometimes need to help it to handle specific task. But still, there're a lot of pre-defined things, so there's no need to reinvent the wheel ;)