if you could specify the precise name og the 3G dongle, perhaps we can tell

Maybe. Without the model number it's kind of hard to tell. I opened up a way to get sakis3g to run on SliTaz, which can detect, switch and run most 3g modems, but you do still get some modems that not even sakis3g can work with.

Using the Sakis3g method also requires you to download a couple of files and packages before installing SliTaz. I describe the whole thing step by step @ http://forum.slitaz.org/index.php?p=/discussion/2273/the-sakis3g-attempt-working