In case anyone needs them, here are the un-documented CnS commands to retrieve the SIP user/password.
//Get chap user
const char CMD_CNS_NVM_GetSipUser[] = {0x7E ,0x00 ,0x0C ,0x2B ,0x00 ,0x10 ,0x33 ,0x01 ,0x00 ,0x00 ,0x00 ,0x00 ,0x01 ,0x00 ,0x02 ,0x01 ,0x3E ,0x7E};
const char CMD_CNS_NVM_GetSipPass[] = {0x7E ,0x00 ,0x0C ,0x2B ,0x00 ,0x10 ,0x33 ,0x01 ,0x00 ,0x00 ,0x00 ,0x00 ,0x01 ,0x00 ,0x02 ,0x03 ,0x8A ,0x7E};