Operating system name and version: Ubuntu 16.04
Version of smsd: Smsd v3.1.21
Smsd installed from: sources
Name and model of a modem / phone: ZTE K3571-Z
Interface: USB ( /dev/gsm2-3 -> ttyUSB2)

I have disabled the modems flashmemory interface by executing the following AT-command: AT+ZCDRUN=8
The modem is being detected as Bus 002 Device 009: ID 19d2:1010 ZTE WCDMA Technologies MSM K3571-Z


I am trying to get smstools up & running on the setup mentioned above, with the config file listed below:

# Global configuration devices = modem1 loglevel = 5 # logfiles stats = /var/log/sms/stats logfile = /var/log/sms/smsd.log # Default queue directory = /var/spool/sms outgoing = /var/spool/sms/outgoing checked = /var/spool/sms/checked failed = /var/spool/sms/failed incoming = /var/spool/sms/incoming sent = /var/spool/sms/sent # do not set report folder, let status report files saved in incoming #report = /var/spool/sms/report delaytime = 2 errorsleeptime = 10 blocktime = 180 autosplit = 3 #receive_before_send = yes incoming_utf8 = yes # Queue configurations [queues] modem1 = /var/spool/sms/modem1 # Modem configurations # Modem name: modem1 # Modem type: Wavecom USB [modem1] #init = AT+CNMI=2,2,0,1,0;+CMEE=1 device = /dev/gsm2-3 baudrate = 115200 incoming = yes report = yes queues = modem1 #pin = 1234 decode_unicode_text = yes cs_convert = yes

This happens when I try to send a message:
2017-09-01 16:25:31,2, smsd: Smsd v3.1.21 started. 2017-09-01 16:25:31,2, smsd: Running as root:root (0:0). 2017-09-01 16:25:31,4, smsd: File mode creation mask: 022 (0644, rw-r--r--). 2017-09-01 16:25:31,5, smsd: Outgoing file checker has started. PID: 2930. 2017-09-01 16:25:31,5, modem1: Modem handler 0 has started. PID: 2932. 2017-09-01 16:25:31,5, modem1: Serving queues: modem1 2017-09-01 16:25:31,5, modem1: Using check_memory_method 1: CPMS is used. 2017-09-01 16:25:38,5, smsd: SMS To: 40737000000. Moved file /var/spool/sms/outgoing/send_Yi06xv to /var/spool/sms/modem1 2017-09-01 16:27:29,3, modem1: Modem is not ready to answer commands (Timeouts: 22) 2017-09-01 16:29:26,3, modem1: Modem is not ready to answer commands (Timeouts: 44) 2017-09-01 16:31:23,3, modem1: Modem is not ready to answer commands (Timeouts: 66) 2017-09-01 16:33:20,3, modem1: Modem is not ready to answer commands (Timeouts: 88) 2017-09-01 16:35:19,3, modem1: Modem is not ready to answer commands (Timeouts: 110)

The modem works on a windows machine and while connected on the Ubuntu PC I get the occasionally blinking blue light which should mean it's registered on the network. Also if I call the sim number inside modem it rings.

What should I do next? where could the problem be?

You could try different baudrates, and the setting rtscts = no if it helps.

Have you tested the modem with some other program, like Minicom?