This allows accessing a resource on a remote OBi, without needing to use the AA. The most common application is making PSTN calls via an OBi located in another country, though there are other useful scenarios.
For example, your speed dial 2 is set to the OBiTalk number of another OBi and you dial 2*3456789. The call is sent to the remote OBi via OBiTalk. If his/her InboundCallRoute accepts your number as trusted, the call is then routed to e.g. the Line port, 3456789 is dialed, and your call is connected.