ess important that SP X can port the DID numbers of your engineering division (currently owned by SP Y). Changing the engineering DID numbers might have little impact to your business and be worth the trade-off to get SIP trunk service from SP X for your entire organization. Regional or Geographic Boundaries SIP trunks are often touted to have no geographic dependency as it is all IP traffic and therefore can be routed anywhere regardless of geographic boundaries. This is technically true, but nevertheless geographic implications of routing voice calls are independent of TDM or IP traffic. One implication is that of DID number portability discussed in the previous section. DID numbers can likely not be ported across international boundaries. Outgoing calls from your enterprise might have similar considerations. For example, con- sider a German-owned bank with offices in both Germany and France. The campus site with the central SIP trunk is in Germany. When an employee in the branch in a French town calls a local customer in the same town, routing that call via the centralized SIP trunk in Germany makes an international call out of what is essentially a local call. Because of hand-offs between SPs, this is considered an international call and using a centralized SIP trunk for this call path is most likely not cost-effective. If both towns were in the same country, the exact same call path (that is, the distance between the loca- tions) would more likely be cost-effective. Tip Evaluate the cost-effectiveness of local calls against your planned SIP trunking model. Ensure that you bring SIP trunks into the optimal number of sites into your network. 90 SIP Trunking Regulatory Considerations When crossing geographic boundaries, you also need to keep in mind regulatory consid- erations. Consider again the German bank example given in the previous section. Although the call routing described might not be cost-effective, the call path from a French branch office to a local customer via a German SIP trunk is still possible