Some voip providers allow multiple registrations on the same account, most do not. It is possible to link two OBi devices together in a "master/slave" relationship. The "master" has the SIP services configured on it, the "slave" receives incoming calls and makes outgoing calls via the "master" OBi. The two are linked by the OBiTALK network, which is free to use by any OBi device.
master OBi 200123456
Assumes that your SIP provider is on sp1.
Voice Services > SP1 Service > X_InboundCallRoute:
{>nnnnnnn:ph,pp(ob200654321)}
"nnnnnnn" is whatever appears in this value (Oleg method):
Voice Services > SP1 Service > SIP Credentials > AuthUserName
Voice Services > OBiTALK Service > InboundCallRoute:
{(200654321)>(xx.):sp1},{200654321:aa},{ph}
slave OBi 200654321
Look in:
Physical Interfaces > PHONE Port > OutboundCallRoute for this rule:
{(Mpli):pli}
Delete it and replace it with this rule:
{(<ob200123456*>(Mpli)):pp}
Voice Services > OBiTALK Service > InboundCallRoute:
ph
If both OBi devices are in the same account, the OBiTALK portal will have put them in each others' Circle of Trust. If so, then delete any settings in both devices here:
Voice Services > OBiTALK Service > InboundCallRoute
and replace with the settings shown above.
EDIT: The slave OBi can be anywhere in the world, so careful thought needs to be given to 911 calls. If you wish the slave OBi to be able to dial 911 via the master OBI, then remove 911 from the slave OBi's Phone Port OutboundCallRoute and put it in its Primary Line DigitMap. If its Primary Line is SP1 Service, then 911 needs to go into Service Providers > ITSP Profile A > General > DigitMap.