I don't think you get a voucher with will call, you may get an email confirmation, but it can not be used to get the DDE card...you'll need an actual voucher or pass.
Actual activated passes will not be delivered to your home, will call is the same as a voucher, only they don't actually mail you a voucher...they keep it on record in their computer and issue the pass when you go to a will call window.
If you opt for a voucher, it will be delivered to your home, but it will be traded in for a real pass when you go to guest services at WDW.