@Blaizzen: yes I took the 3g module

@Venemo: it's externally just alike the one I ordered, and has the same features, apparently. But you're right, that's a point I can enforce when asking for rembursement.

@Linuxeventually: thanks for help. The device's radio module seems to work, at least partially. It shows the carrier's name on display, field bars in status area, and apparently awakes when I try to phone it, showing the called Id. Though, there is no way to answer the call, and no way to place a call, since there's no dialer.
Based on these findings, I think the unit is lacking of a proper software. Maybe they installed the wrong android version. Strangely enough when I go and search for info, it says model m7002, firmware version 1.5.264 kernel 2.6.28 ferris@linux-server #SVN-r370 build number m7002-eng 1.5 CUPCAKE eng.ferris.20100609.152050 test-keys.
All these things mean nothing to me, except that the m7002 seems yet another tablet model with win ce 6.

@Duncan: I'm quite confident the apn I used for each sim card are the right one. I took them from the carriers' sites, and from some Italian android wikis.

Thanks all, now back fiddling with the damn'd thing, before I send it back to that guy

EDIT: apk files get installed (though pacman didn't start )