RegExpression for allowing #-###-###-#### or ###-###-#### formats Phone Numbers only

Hi,
I wanted an RegularExpression that should allow user entering Phone Numbers in #-###-###-####  or ###-###-#### format only. I already have implemented RegEx [1] for the  #-###-###-#### format. What changes do I need to make to my existing RegEx so that it would only allow/accept Phone Numbers in the above 2 formats?
Thanks in advance!!
[1]
@"^\d{1}-\d{3}-\d{3}-\d{4}$"
- Vipul
...