To be honest, in this day and age, there are perhaps more suitable means to obtain internet access via satellite than dial-up via COM port.
Can you give an example?
Fitted systems tend to start well into 5 digits.
This is for airborne use, not ground use.
Is there a reason why you need do use a COM port ?
The phone is RS232.
One could use one of the "RS232 over TCP/IP" boxes, and then any ethernet device could talk to it, in principle, but that is more hassle.