The mobile Internet&rsquo;s growth is a trend on par with the mass adoption of the personal computer, Cramer said. Smartphones, which handle everything from voice to video to data, soon will be as ubiquitous as the PCs we now take for granted. This means that the related companies, and their shareholders, should see gains for many years to come. To track the trend, Cramer created the Mad Money Mobile Internet Index, a group of 21 stocks at the heart of the industry. The index starts at 100, and its ri