The Telit plugin currently only works with USB devices; in order to support RS232 devices the plugin should be able to check for "vendor strings" in addition to the USB-only "vendor ids".
https://lists.freedesktop.org/archives/modemmanager-devel/2017-March/004079.html
Fix pushed to git master as 8664b2a38ac71428a5bbc3d89fbef3f68aea6430.
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