Operating system name and version: Gentoo
Version of smsd: 3.1.15
Smsd installed from: sources
Name and model of a modem / phone: Sierra MC8775
Interface: serial

config:


2013-02-14 15:53:18,6, GSM1: Sending SMS from to 48XXX 2013-02-14 15:53:18,6, GSM1: Checking if modem is ready 2013-02-14 15:53:18,7, GSM1: -> AT 2013-02-14 15:53:18,7, GSM1: Command is sent, waiting for the answer 2013-02-14 15:53:19,7, GSM1: <- OK 2013-02-14 15:53:19,6, GSM1: Pre-initializing modem 2013-02-14 15:53:19,7, GSM1: -> ATE0+CMEE=1;+CREG=2 2013-02-14 15:53:19,7, GSM1: Command is sent, waiting for the answer 2013-02-14 15:53:19,7, GSM1: <- OK 2013-02-14 15:53:19,6, GSM1: Initializing modem 2013-02-14 15:53:19,7, GSM1: -> AT+CMGL 2013-02-14 15:53:19,7, GSM1: Command is sent, waiting for the answer 2013-02-14 15:53:20,7, GSM1: <- OK 2013-02-14 15:53:20,7, GSM1: -> AT+CSQ 2013-02-14 15:53:20,7, GSM1: Command is sent, waiting for the answer 2013-02-14 15:53:20,7, GSM1: <- +CSQ: 17,99 OK 2013-02-14 15:53:20,6, GSM1: Signal Strength Indicator: (17,99) -79 dBm (Good), Bit Error Rate: not known or not detectable 2013-02-14 15:53:20,6, GSM1: Checking if Modem is registered to the network 2013-02-14 15:53:20,7, GSM1: -> AT+CREG? 2013-02-14 15:53:20,7, GSM1: Command is sent, waiting for the answer 2013-02-14 15:53:21,7, GSM1: <- +CREG: 2,1,A8D4,3DE2 OK 2013-02-14 15:53:21,6, GSM1: Modem is registered to the network 2013-02-14 15:53:21,6, GSM1: Selecting PDU mode 2013-02-14 15:53:21,7, GSM1: -> AT+CMGF=0 2013-02-14 15:53:21,7, GSM1: Command is sent, waiting for the answer 2013-02-14 15:53:21,7, GSM1: <- OK 2013-02-14 15:53:21,7, GSM1: -> ATE1+CMGS=28 2013-02-14 15:53:21,7, GSM1: Command is sent, waiting for the answer 2013-02-14 15:53:22,7, GSM1: <- > 2013-02-14 15:53:22,7, GSM1: -> XXX▒ 2013-02-14 15:53:22,7, GSM1: Command is sent, waiting for the answer 2013-02-14 15:53:22,7, GSM1: <- XXX +CMS ERROR: 304 (Invalid PDU mode parameter) 2013-02-14 15:53:22,5, GSM1: Verify PDU: OK 2013-02-14 15:53:22,7, GSM1: -> ATE0 2013-02-14 15:53:22,7, GSM1: Command is sent, waiting for the answer 2013-02-14 15:53:23,7, GSM1: <- ATE0 OK 2013-02-14 15:53:23,3, GSM1: The modem answer was not OK: XXX+CMS ERROR: 304 (Invalid PDU mode parameter) 2013-02-14 15:53:23,5, GSM1: Waiting 10 sec. before retrying

Have you tried sending without smsc_pdu setting?

Also, is the number of SMSC surely correct? In many cases it is not required, so trying without it could be reasonable.

If the sending still does not work, you could try if the SIM can send messages when it's used in the regular phone device.