You can change the way the field is formatted by going to Tools > Define Fields > Choose the fields you're interested in and choose Edit Fields.
On page two of the edit field options you can define the field format.
According to this KB http://kb.act.com/app/answers/detail/a_id/14024 : "Use 'place holders' to specify a Field format. Available place holders are: Alpha/Numeric (%), Numeric (#), Alphabetical (@)."