For the E1752 model the network manger applet will not pop up unlike other dongles as it also acts as a storage device.

sudo apt-get install usb-modeswitch

Put this in /etc/usb-modeswitch.conf

# Huawei E1752
DefaultVendor = 0x12d1
DefaultProduct = 0x1446
TargetVendor = 0x12d1
TargetProduct = 0x1001
MessageEndpoint = 0x01
MessageContent = "55534243000000000000000000000011060000000000000000000000000000"

Optionally: network manager > mobile broadband > o2 pay as you go > ... enter your own pin on the end

sudo usb_modeswitch

Now you should be able to:

python
import serial
ser = serial.Serial('/dev/ttyUSB0')
ser.write("at\r")
ser.readline()