This speed dial format works fine with an OBi110:
li(xxxxxxxxxxx)
It sends the call directly to line with no reference to digit maps etc. I cannot see any reason for it not working with the OBiLINE adapter. It may simply be that Obihai forgot to include this function in the software.
You might try this format in the speed dial:
**70xxxxxxxxxxx
It does not send the call directly to line, but rather through the digit maps etc as if you were dialling the number through the Phone Port.