Mandriva 2009.0:
Smsd v3.1.21:
Smsd installed from: sources
Interface: serial to USB adapter Prolific 2303 (embedded into device)

I encounter one problem with the above device.
Device present a busy tone while is communicating via serial interface. This is normal. If I connect with Minicom, when exit, device returns to the normal functionality. This include checking and sending sms by typing AT commands the same way smstools is doing.
However, in smstools case, after stopping smstools, the normal functionality does not return. Device continue to present busy tone. It remains probably hanged.
The only way to restore normal functionality is to power cycle the modem or server restart.

Question is:
What can be the difference in communication between Smstools and Minicom and what can possibly "upset" my modem?

Action done:
- ps check, no process left active.
- increase communication_delay to 100 and then to 40000. However I noticed that ATE0 ignore communication_delay. I wanted to check the behavior if only AT command is sent.

2017-12-14 10:18:19,2, smsd: Smsd v3.1.21 started.
2017-12-14 10:18:19,2, smsd: Running as root:root (0:0).
2017-12-14 10:18:19,4, smsd: File mode creation mask: 022 (0644, rw-r--r--).
2017-12-14 10:18:19,5, GSM1: Modem handler 0 has started. PID: 16672.
2017-12-14 10:18:19,5, GSM1: Using check_memory_method 1: CPMS is used.
2017-12-14 10:18:19,5, GSM1: Using communication_delay between new commands 40000 milliseconds.
2017-12-14 10:18:19,5, smsd: Outgoing file checker has started. PID: 16671.
2017-12-14 10:18:19,6, GSM1: Checking device for incoming SMS
2017-12-14 10:18:19,6, GSM1: Checking if modem is ready
2017-12-14 10:18:20,6, GSM1: Pre-initializing modem
2017-12-14 10:18:54,2, smsd: Smsd mainprocess is awaiting the termination of all modem handlers. PID: 16671.
2017-12-14 10:18:54,2, GSM1: Modem handler 0 terminated. PID: 16672, was started 17-12-14 10:18:19, up 0 min.
2017-12-14 10:18:54,2, smsd: Smsd mainprocess terminated. PID: 16671, was started 17-12-14 10:18:19, up 0 min.

- I have check various communication settings combinations without success. (rtscts, send_delay, communication_delay, send_handsake_select)

- My desired usage is to have delaytime=60 or more and keep_open=no. What I want is to achive both functionality, call through asterisk and sending SMS. The configuration will be used for private use, so there is a little impact of overlapping.

Thank you for your support.