NEW YORK ( TheStreet) - The days of ad-free Android Gmail may be numbered, as Google ( GOOG) has reportedly put the steps in place to switch-on advertisements in its free email program for smartphones and tablets. In a detailed tear down of the recently released Gmail app update (version 4.6) Android Police discovered a number of lines of code which mention the possibility of ads in the new software. Desktop and laptop computer versions of Gmail have contained ads for years,with rotating ads displayed on the top line of the Web page. The ads are chosen based on information Google gathers from the messages in your mailbox. The new software suggests there will be different classes of ad properties it will have, including "toasts", "teaser", "sender header", "ad header", "ad border", and "ad view." That means the ads could show up in different forms and locations in the software. Gmail 4.6 will allow users to save an advertisement as a message. Other changes to the Gmail app include a new unsent message warning, the removal of a "Cancel" message button as well as new dark colored icons. --Written by Gary Krakow in New York. >To submit a news tip, send an email to: email@example.com.