5 gsm modems in one computer?

Hi guys...

please help.

i need to set up 5 Nokia 30 gsm modems in one computer.

my problem here is, since nokie 30's cable is a serial, and a computer has
only 2 com/serial port, how am i going to plug in the other 3 gsm modems?

please provide solutions, ways how to set this up.

many thanks for your time.

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Best regards,
David Ang