Will a customer with an outstanding balance 1 year or older on a residential account qualify for debt forgiveness if (s)he only signs up for new mobile service during the promotional period?

Yes. Customers with outstanding balances on residential accounts will have their debt forgiven if they sign up for mobile service.
Customers can sign up for any new service and have their debt (1 year and older) on any type of account forgiven. The new service does not need to be the same type of service.