The SysManSMS Server works very well with virtual server products like Hyper-V, VMWare and others.
The best option would be to use a modem with built-in LAN interface, such as the "SysMan 2G/3G/4G LAN modem with Watchdog". This modem can be purchased from SysMan directly or through resellers.
If you have a serial modem, you should use a Serial-over-IP solution like the Moxa nPort 5110.
If you have a USB modem, you should use a solution like anywhereUSB.