If you are on the basic home plan of Rs.250, then the best way not to exceed the 0.4gb limit is by turning off the images/pictures function on your web browser.
If you are using IE Goto Tools>Options>Advanced>Multimedia, uncheck show pictures.
For Firefox>Tools>Options>Content>uncheck show images.
From now on you can spend twice the amount of time surfing the net. If you like to view a particular image, right click and then click show picture in IE and show image for Firefox. When I first used this service, I would exceed the limit by surfing 40hrs, now I use atleast 80 hours.
I havent had any major problems yet with this one. It usually connects the first time, maybe sometimes it doesnt but almost every other service has the same problem.
I recently called the support guys and you dont have to wait forever to get a real person on the line. The support guys are pretty helpful. Have used this service for about six months now and no major hiccups.
Last but not the least, I didnt expect this sort of a service from BSNL!!
Happy Surfing!