Hi, I checked resolv.conf and strangely found inside this content:
This is pretty strange, since I've never modified this file, or specified DNS servers elsewhere. Maybe KPPP inserted them on my first connection through my mobile? This would explain why my mobile connection got no problem, too.
Anyway, I solved the problem adding the "disable local nameservers" option in kppp... I'll look forward to solve the problem once for all this evening.
Thanks for the clue!