10mb
10000kb
This depends on what kind of websites you are visiting. If you're only going to simple HTML or PHP sites, at about 100kb each, then 3gb would last about a month. If you're going to media-rich pages at 10mb (or 10000kb) each, with mp3's integrated (such as myspace), of viewing a lot of photos, you're looking at 2 weeks. If you're constantly streaming youtube videos, or using other flash apps like yoville, then probably a day or 2.