GSM Modems are industry type devices, and may not fully support some of the new SIM cards created for modern mobile phones. If you during installation of the SysManSMS Server see such problems, the Server will stop, and a typical error code in the SysManSMS.log file will be:

ERR-120-1 Can't get number of SIM locations in unit

You should first of all try to upgrade your SysManSMS Server to the latest release. If this does not help, you may have a unsupported SIM card.
Please see SIM Card Test Document for layout pictures of some tested  SIM cards for the Sierra Wireless FXT series.