Hi,
You can define a display format pattern of "num{999-999999-999}" that will add the hyphens in once they leave the field, or maybe having three fields with the comb option set and hyphens between them would suit more?
You can use the null display pattern to display any sort of text in a numeric, date, or whatever field. Have a look at this sample, Adobe LiveCycle Designer Cookbooks by BR001: Adding Ghost Text to LiveCycle Designer form
Regards
Bruce