This post is related to playSMS and Kannel, how to configure Kannel when you know that the device file names aren’t persistent.
When USB GSM modem plugged to a server Linux kernel assigned dynamic device file /dev/ttyUSB*, such as /dev/ttyUSB0 or /dev/ttyUSB1. For example, USB GSM modem with 2 ports will then be assigned to /dev/ttyUSB0 for port 1 and /dev/ttyUSB1 for port 2.
Problem starts when we unplug the GSM modem and re-plug back afterwards. Linux kernel will then assign different device file to it, was /dev/ttyUSB0 now /dev/ttyUSB2 and was /dev/ttyUSB1 now /dev/ttyUSB3.