The ones provided with the distribution do not work. They must be disabled from the system settings, Hardware drivers menu. Then, I installed the “linux-backports-modules-intrepid” package (aptitude install linux-backports-modules-intrepid) and rebooted. The wireless works pretty fine

In order to make the Alice Gate 2 plus WiFi modem working (with the plain settings it does not work fine: some pages display correctly, some other timeout or/and do not display at all), I modified some of the parameters of the TCP/IP stack as suggested here. The modifications made to the /etc/sysctl.conf consist in adding the lines

net.ipv4.tcp_syncookies = 1 
net.ipv4.tcp_window_scaling = 0 
net.ipv4.tcp_ecn = 0

at the end of the file and restart the network (reboot). This is to be done once and forall.