How to use PowerShell for Active Directory tasks

How would I do the following in PowerShell?

1.  I want to edit the Telephone Number, Mobile and Fax properties in multiple users.
2.  I only want to edit those properties if any or all of them are populated with a dash ( - ).
3.  If those properties are populated with a dash ( - ), then I would like to remove it and leave the property empty.  

This is meant to be done to all users in a domain with 2 thousand users and has a structure of many OUs.

Thanks!!