Huawei E220 modem. Warrenty will be voided ;)
Female SMA RF connector
7db omnidirectional magnetic base antenna with 3m cable (or what suits your price range). Mine was 200 Bucks. ($20)
1: Remove the SIM tray and faceplate covering the signal LED with a small screwdriver. (Plastic is better as not to scuff)
2: Remove the Torx screw just next to the LED and carefully unclip the cover.
3: Once opened, remove the clear plastic standard antenna. Opposite to the USB port.
4: Strip and solder the SMA cable to the pins where we removed the plastic antenna.
5: Heat up a screwdriver with the same width as the tail, then melt a space for the cable to sit outside the housing.
6: Put it all back together, test, then superglue.
I have kept the tail short so i can travel with the modded antenna.
Happy Hacking :)