Emacs can even be used to communicate with serial ports! Hence, it can replace softwares like minicom, hyperterminal, putty etc. that are used for serial port communication.

Making a connection is simple,

M-x serial-term

enter port name and baud rate, and it's connected!

E.g. In Linux based systems, if we need to connect to a GSM modem, find its port name by listing /dev/serial/by-id/

ls -l /dev/serial/by-id/

which will show the symbolic link to the serial port to be used. Suppose the name is /dev/ttyUSB3

Then, using that name with the default baud rate (9600 bps) connects to the modem. The settings can be changed at runtime without requiring to reconnect to the serial port.

And we may issue the standard AT commands

at
OK
at+cpin?
+CPIN: READY

OK
at+csq
+CSQ: 14,99

OK
at+cmgf=1
OK