Disclaimer: This is totally untested, so please don't shoot the messenger if there are surprises.
I think I've come up with an approach that effectively adds the LINE Port of a remote OBi110 to an OBi100. The PrimaryLine of the OBi100 is effectively set to the remote 0Bi110 LINE Port. Both units can still use their local SP1, SP2, and OBiTALK Services in the usual manner. A relatively small number of changes are required:
OBi100
Physical Interfaces -> PHONE Port -> DigitMap:
([1-9]x?*(Mli)|[1-9]|[1-9][0-9]|**0|***|**1(Msp1)|**2(Msp2)|<**8:99*>(Mli)|)**9(Mpp)|<99*>(Mli))
Physical Interfaces -> PHONE Port -> OutboundCallRoute:
{([1-9]x?*(Mli)):pp},{**0:aa},{***:aa2},{(<**1:>(Msp1)):sp1},{(<**2:>(Msp2)):sp2},{(<**9:>(Mpp)):pp}
User Settings -> User Defined Digit Maps -> User Defined DigitMap2:
Label : li
DigitMap : (xxxxxxxS4|1xxxxxxxxxx|xx.)
Speed Dial 99 : 290123456 (290123456 = OBi110 OBiTALK Number)
OBi110
Voice Services -> OBiTALK Service -> InboundCallRoute :
{(290654321)>(Mli):li},{(290654321):aa},{ph} (290654321 = OBi100 OBiTALK Number)