You mentioned you have a line port, then it must be an OBi110. Assuming you enter using unit web interface. If you use the portal, you get the idea.
If line port is all you need,then look here:
Physical Interfaces->LINE Port->InboundCallRoute = Insert here
Insert something like this:
{(x.5145551212|x.5145551213|x.5145551214):aa},{pp(ob290000000),ph}
Explaination:
3 different numbers can hit the AA, everything else hits an OBiAPP, and phone
You can simplify it by removing the pieces which you don't need. You may also consider implementing the speed dials with this approach. It will save you time. I like to set up the speed dial like this **25145551212. Note that I prepend which service provider (**2) that I want to use to make the outgoing call. When you hit the AA press the speed dial "number" +"#".