SCI

I am having an issue with a modem I am using on a V120. I am able to make it work just fine on a V1040 and a V1210. The issue is the command for deleting a text message (AT+CMGD). For some reason the V120 uses the command AT+CMGD=01 while the V1040 and V1210 use the command AT+CMGD=1 when deleting a text message. I have tried all of the different modems configs on these PLCs and the command is the same on both the V1040 and V1210 but the V120 adds the "0" for some reason and when this happens the modem responds with "ERROR" and does not delete the message from that memory slot. Why does the a V1040 and a V120 configured for the same modem behave differently.