MSC-to-PSTN voice traffic. Mobile-to-mobile calls within our own system are handled through direct MSC-to-MSC links. We can save additional cost by establishing direct links to the MSCs of other car- riers in the same region, avoiding the PSTN. To do this, we need to program our MSCs with the mobile identification number (MIN) ranges used by the other carrier, and the other carrier needs to do the same with the MIN telephone numbers assigned to our customer's user terminals. Least-cost routing inside the MSC switch will use the direct lines first and route the call through the PSTN for overflow. Except for private voice networks and mobile-to-mobile calls handled separately, voice call originations from a wireless telephone in the MSC region go directly from the MSC to the PSTN. 2 Call terminations to a user terminal's home MSC come directly from the PSTN to the MSC. Calls to roaming user terminals come into their home MSCs from the PSTN, routed by the telephone number of the user terminal. Roamer terminations for calls coming in to a local access transport area (LATA) where the user terminal is roaming to a differ- ent MSC but is in the same region should be routed on inter-MSC trunks. We traffic engineer these trunks to reduce costs, but overflow will add to the MSC-to-PSTN traf- fic load. If we do not transport these calls separately to their visitor MSCs, then they go back out to the PSTN to be sent to their destination, where they come back in from PSTN to the visiting MSC. The cost savings we realize by using our own MSC-to-MSC transport for roamer terminations and mobile-to-mobile calls as well is not the incre- mental cost of MSC-to-PSTN transport. It is the PSTN charge for each call that we hope to save by carrying our own calls on our own facilities from one MSC to another. The situation for long distance (inter-LATA) roaming is different. The latest version of ANSI-41, ANSI-41D, supports a method that prevents tromboning. When the Sig- naling System 7 (SS7) network contacts the home MSC and home locati