I'm wondering if it's possible on a VoIP system (specifically Asterisk) over SIP trunks to redirect a call back out to the PSTN to no longer be routed through the PBX.
What I'd like to do is see about brokering connections between two 10 digit numbers on the PSTN, but once the connection is brokered no longer be maintaining it (eg: if the PBX has a service interruption, the call stays online).
I know it's possible to do something similar with SIP, but not too sure if I can do that out on the PSTN.
The signalling bits to do this are certainly there (part of either the SS7 or PRI protocols. I can't remember which), but whether or not you'll be able to convince a telco to permit you to do this is a completely different matter. Things get complicated real fast with regards to billing and who is responsible for what.
You may want to re-evaluate your need for this functionality.