If your gateway is not sending messages and in modem log you've got following error:
Wed 2016/03/09 17:01:26 gammu-smsd[2275]: Error sending SMS: No SMSC number given. Provide it manually or use the one configured in phone. (EMPTYSMSC[31])
We suggest to put the SMSC number in sms daemon configuration, it should solve that issue. To do so:
1) Log in via SSH
2) edit config file:
(modem #1) nano /etc/gammu-smsdrc1
(optional for modem #2) nano /etc/gammu-smsdrc2
3) At the bottom of the file add (we advise to add this after line with deliveryreports):
smsc = xxxxxx (where xxxxx is your smsc number)
Please also add empty line at the end of the file.
4) save and exit
5. Restart modem software
a) Enter webGUI > tab Maintenance
b) disable selected Modem and press "Save" button
c) enable selected Modem and press "Save" button