To make the POTS line the default outbound line set:
Physical Interfaces --> Phone Port --> Primary Line --> PSTN Line
Then to dial a call using SP1, which you said you configured for voip, you would preface the call with **1, otherwise the dialed call will go on the PSTN Line
I don't believe you will do any call bridging or forwarding without changing the default settings.
Incoming calls will come to you via SP1, SP2 (if configured), or the Line Port. Each of these services have a default configuration for "Ring Profile" which are defined under Ring Settings.... Ring Profile A and Ring Profile B. The OBihai Admin Guide says Ring Profile A matches the ringing in the U.S., Ring Profile B matches the ringing in Australia. Within each Ring Profile they have defined 10 different ringing cadences for distinctive ringing. There is a configuration setting under SP1, SP2, Line Port, OBiTalk Port. In your case you are receiving calls via SP1, and Line Port
Voice Services --> SP1 Service --> X_DefaultRing
and
Physical Interfaces --> Line Port --> X_DefaultRing
In your default configuration, these settings are set by default to Ring Pattern 1. You can change the setting to whichever pattern you wish.
From OBi Device Administration Guide:
Default ring pattern number to ring the PHONE port for incoming calls on this trunk that are routed to the PHONE port according to the InboundCallRoute of this service. The ring pattern is taken from the selected Ring Profile. Valid choices are 1-10http://obihai.com/docs/OBiDeviceAdminGuide.pdf