Looks like a straightforward translation to me. '0' goes to '\d', '9' goes to '\d?', and so on. I'd do a one-to-one translation first and then run it through some an optimizer ('\d\d\d\d' becomes '\d{4}', for instance). Put the resulting string in a qr// and pass it back, ready to be matched.

Better yet, run the result through YAPE::Regex::Explain to show them how to do it properly. Like many things in VB, input masks are too simple for their own good, and you pay the price for this simplicity with overall more complex code.