until such time that you are satisfied the SIP trunk service is stable and that possible failures are taken care of in your network design. At this time your SP needs to port the DIDs of the new user community to join the SIP trunk. This might be a single phase of porting, or potentially several phases, depending on the plan you have formulated during the planning step. Best Practices This chapter concludes with a summary of best practices for planning, preparing, and deploying SIP trunking in enterprise and SMB networks, giving clear and practical advice on how to approach a SIP trunk deployment in your network. Providers Best practices in the area of choosing a provider include Look for a provider that owns the physical delivery medium (last mile) to your premises along with the service. The last-mile provider is the only one who can guar- antee QoS. If keeping your existing DID numbers is important to your business, your most like- ly provider is the same one with whom you get your current PSTN service. Evaluate SIP trunk service offerings carefully-it's an unregulated service and offer- ings and pricing can vary greatly. Always do a proof-of-concept trial before installing a SIP trunk into your production business network. Evaluate SIP trunk offering features against your current TDM service and make sure you get all the features that are important to you. Chapter 11: Deployment Steps and Best Practices 257 Deployment Best practices in the area of deployment include the following: Plan carefully and don't rush into a production deployment until you're certain of what you're getting. Use the earlier part of this chapter to help you through the plan- ning steps. Define the user communities or sites you will deploy in the different phases of the deployment. For all but the smallest of networks composed of no more than a single or a handful of sites, this is a multiphased rollout plan. Decide on the call flows included in each phase of deployment, for example inbound, outbound, long distance, contact center, or g