At EuroPython, I happily took advantage of the prepaid SIM card that you could order together with your ticket. However tethering with Wind (Italy) was not to work that simply. On Debian Wheezy I ended up with the following error:

[...]
--> Modem initialized.
wvdial: utils/wvtask.cc:409: static void WvTaskMan::_stackmaster(): Assertion `magic_number == -0x123678' failed.

A bit of astute googling reveals that libwvstreams needs to be downgraded.

$ aptitude versions libwvstreams4.6-base # or apt-cache policy libwvstreams4.6-base
Package libwvstreams4.6-base:
p A 4.6.1-1                                       stable                    500
i A 4.6.1-4                                       testing,unstable          500
$ sudo aptitude install libwvstreams4.6-base=4.6.1-1

Tadam! wvdial now works. The same configuration as last year seems to do the trick (though on Fedora 16, the Network Manager's Mobile Broadband tool was easy to set up with Wind without  bothering with wvdial.)

[Dialer wind]
Modem Type = USB Modem
Modem = /dev/ttyACM0
Username = "wind"
Password = "wind"
Init6= AT+CGDCONT=1,"IP","internet.wind"