The idea to monitor and communicate with the device is the same on both OS, what changes is the device name. For Linux the devices name to use can be found with

sudo dmesg | grep tty

Normally is/dev/ttyUSB0,  /dev/ttyUSB1,  /dev/ttyUSB2,  /dev/ttyUSB3,  /dev/ttyUSB4 for Linux, and on my Mac osX Lion I have

ls -l /dev/cu.*
crw-rw-rw- 1 root wheel /dev/cu.HUAWEIMobile-Diag
crw-rw-rw- 1 root wheel /dev/cu.HUAWEIMobile-Modem
crw-rw-rw- 1 root wheel /dev/cu.HUAWEIMobile-Pcui

For this purpose lets assume a generic device name <DEVICE>, that it is either a Linux or osX tty. First we need to find out which of the several terminal is used for communication, and for that we need to open monitor terminals for each of the devices.

Terminal 1: cat /dev/<DEVICE1>
Terminal 2: cat /dev/<DEVICE2>

and in another terminal we send an AT command like this:

echo "ATi^M" > /dev/<DEVICE> #(note: ^M is ctrl+v+m)

And one of the monitor terminals above will show something like this:

Manufacturer: huawei
Model: E353
Revision: 11.810.09.40.156
IMEI: 86816500xxxxxxxxx

In my mac the terminal that I need to use is /dev/cu.HUAWEIMobile-Pcui and in Linux is /dev/ttyUSB0.