I got my confirmation the other day... from the email:
The discount will be 10% on all monthly recurring charges. Please be advised that this discount will apply to all currently active lines on the account, as well as any additional lines activated in the future. You will see your discount credits displayed in the "Adjustments to Bill" section described as "Corporate Volume Discount" on your billing invoice.
Also from the email... and a reason I'd probably hurry to do this:
I apologize for the delay in completing this request, as our volumes are
higher than anticipated.