This Ringless Voice Mail feature is not intended to support broadcast marketing from your Infusionsoft account. Don’t use it to send a message to large number of Contacts at one time.
You can use the Ringless Voice Mail add-on to send an average of 3 voice mails per minute, or 180 per hour. If your campaigns send voice mails at a pace faster than 3 per minute then voice mails will be queued and sent on a first-in-first-out basis at the 3 calls per minute pace. If your queue of back-logged voice mails exceeds 180 voice mails then any additional voice mails will not be sent until the backlog is reduced.