Hello,
Why are you attempting to use wvdial? Of course, that's the semi-official way for the Tata Indicom Plug2Surf (as in it's in the manual), but for just about every other phone that you're likely to have, GPRS Easy Connect should work!
You can find a guide to installing it on their website, at *www.gprsec.hu/modules/docs/. Note that it doesn't work for Ubuntu (Kubuntu, Xubuntu, or any of the other *buntus) yet, but there is a workaround - install everything by hand!
The guide is at *www.gprsec.hu/modules/news/view.php?id=260.
Apparently the system supports Airtel at the least, but they don't have Vodafone listed there - annoying, since with Vodafone being an international company, surely they'll have 3G before anyone else? Someone should track down the Vodafone details and post them on the forum there.
That's all folks (power cut),
Cam.Turn
WARNING: DON'T try installing any other software by hand if it doesn't work, as it's VERY likely that you'll break your system. Instead, ask on their forum, or e-mail one of the developers. If it turns out that you HAVE to install it by hand, ask the developers to give you detailed instructions.