I haven't used Kannel specifically but I have used similar modems. When you plug in the modem with the relevant drivers installed it exposes each of the sim cards as an individual port. So on windows you get
COMi, COMi+1.....COMn but not necessarily in increasing order. But the final count corresponds to the number of sim cards. FOr Linux, for most of them you dont need to install any drivers, but note that each interface can be exposed as three consecutive interfaces for example you might get
/dev/ttyUSB0, /dev/ttyUSB1 and /dev/ttyUSB2 point to the same sim card. So for a 16 port modem you end up with 16*3=48 /dev/ttyUSB# interfaces.