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When a business shifts from time-division multiplexing (TDM) to Session Initiation Protocol (SIP) trunks, it can lead to substantial savings for the business. However, doing so is a multifaceted proposition that demands judicious preparation and a great deal of time. In transitioning from TDM to SIP trunks, there are two different telephone number configurations in the mix: Direct Inward Dialing (DID) numbers and toll-free numbers. Toll-free number migration (when enlisting a new carrier) involves much more complexity than addressing DIDs, and is what will be addressed here.

Project Management: The Key Concept

Project management is the most important factor to examine when considering the shift to SIP trunking. A competent and experienced project manager is a must, and can shave weeks off of the process. Such an individual will consider the project timeline as it affects organizational commitments, and will build buffers into the timeline to account for unforeseen problems and avoid financial penalties.

The Project Inventory

All toll-free numbers must be inventoried and documented. One may be surprised to learn that many organizations have no organized record of their thousands of toll-free numbers. All of these numbers and their features, assignments, and call flows are essential to have inventoried for the new carrier to effectively deploy them.

Call Routing

The call routing plan must be designed and configured along with any desired modifications to the new plan. Implementing routing for a toll-free network is a completely different animal than doing so within an in-house platform and requires a substantial amount of time and resources.

The RespOrg Factor

The first step to transitioning the company’s toll-free numbers is to determine the RespOrg, or the organization responsible for maintenance of the toll-free numbers. Many carriers demand that this be done before any other action is taken.


The testing of toll-free numbers can be time-consuming and problematic due to certain aspects of their production environment, but testing and optimization is still possible. It is probably not feasible to test each and every number, but random numbers can be tested from similarly-configured batches.


In scheduling cutovers, coordination between the IT groups executing the cutovers, the business, and the new carrier will be facilitated by the project manager. It is essential that the business customer is engaged in the process of the actual cutover, which will involve careful coordination between the customer, the new carrier, and relevant IT groups.

Post-cutover Cleanup

It is prudent to keep lines of communication between the project team and business customer open for anywhere from a day to a week in order to address any issues that may arise. This is also an opportune time to execute any further testing of time-of-day and day-of-week routing.


This is the process by which the toll-free numbers, TDMs, routing, features, and announcements are discontinued relative to the legacy carrier. This is more complicated than it sounds, and lead times can run into weeks. The challenges relative to migrating toll-free numbers to SIP trunks using a new carrier should not be underestimated. Following these steps judiciously, however, will go a long way toward making the process as painless and cost-effective as possible.

To learn more about SIP trunking, contact thinQ today.