If you experience the following problem:
(example of modem log entry):
Tue 2016/10/04 00:20:12 gammu-smsd: SMS sent on device: "/dev/ttySMSA0" status=111, reference=-1
Field status reports error numbers, which are referenced as CMS errors. Definitions of most of them are available e.g here: http://www.smssolutions.net/tutorials/gsm/gsmerrorcodes/
Error 111 is described as Protocol error, unspecified which basically is a bit..unclear but the issue is pretty sure caused by the SIMcard.
- this error may happen when you send SMS with national characters and don't check "Send as Unicode" in webGUI > menu Compose. Verify if this is the case
- check if the mobiler number you provided is correct
- check is the SIM able to register in network/make calls/send messages/have SMS service enabled?
- check GSM signal strength (usually ~30% is the lowest value for proper message send&receive)
- check with your mobile carrier if this SIM is not blocked somehow, or assigned to one particular device (your old one?)
- ask carrier to 'delete the profile information' of the SIMcard
- check Is this SIMcard capable to work with GSM/3G device? (it can't be CDMA only)