Hi,
The details of values populated is not given but what do you have in the updateflag field is it 'I'. The pattern would be similar to
CLEAR: bapiadtel, bapiadtel_x.
bapiadtel-consnumber = '002'.
bapiadtel_x-updateflag = 'D'.
APPEND: bapiadtel, bapiadtel_x. "Delete entry
CLEAR: bapiadtel, bapiadtel_x.
bapiadtel-consnumber = '003'.
bapiadtel-extension = '77733'.
bapiadtel_x-extension = 'X'.
bapiadtel_x-updateflag = 'U'.
APPEND: bapiadtel, bapiadtel_x. "Update entry
CLEAR: bapiadtel, bapiadtel_x.
bapiadtel-telephone = '06227'.
bapiadtel-extension = '11111'.
bapiadtel_x-updateflag = 'I'.
APPEND: bapiadtel, bapiadtel_x. "Insert new entry
Also you mentioned
...which requires the partner number (which obviously doesn't exist yet)
I think we need the partner first to add, update the related information. Please create the same using BAPI_BPCONTACT_CREATEFROMDATA.
Cheers,
Arindam