Hi.
You should be able to do this if you enable a regular expression validation on the field. The dash won't be hard coded in (unless you setup a client side event to do so, which actually is possible though but I would get the regular expression working first). If you google regular expressions should be able to come up with several sites that should give examples for what the expression should be. Specific coding of client side events is not covered with standard support hours but if you post a similar solution/form on www.betasprings.com ill see if we can assist in helping to determine the javascript function that will cover your needs.
-Chad