1:
For SP1, set CallForwardOnNoAnswerNumber to e.g. SP2(1234) . On your Asterisk system, set up 1234 as a feature code that routes to a DISA. The DISA would answer, ask for a PIN (if desired) and then play dial tone.
Instead, if your SP1 provider supports two or more registrations on the same account, you could have both the OBi and Asterisk register to them. Set up the Asterisk inbound route to delay answering, then send the call to DISA. This method does not route DISA calls through the OBi, so it should be more reliable and have better quality.
2: If your SP1 provider supports multiple registrations as above, or if they permit unregistered (though authenticated) outgoing calls, simply set up a trunk on Asterisk to route the desired calls via your SP1 provider. This does not involve the OBi at all. If this solution is not feasible, please describe the constraints and I'll try to present an alternative.
What Asterisk distribution are you running (FreePBX, etc.)?
Who is your SP1 service provider?
If you have no connection to the PSTN, the OBi100 (instead of OBi110) should work for your application.