If this Nokia is available over serial port (check device manager for virtual ports), then you can use it with "generic" driver.
The are two server parameters (Configuration -> Server Configuration): SMSDriver и SMSDrvConfig.
Example (port COM1, port speed - 9600, 8 data bits, no flow control, 1 stop bit):
SMSDriver=generic.sms
SMSDrvConfig=COM1:,9600,8,N,1,T
Detailed description: https://www.netxms.org/documentation/adminguide/sms-drivers.html#generic-gsm-modem-driver