Android market selling upgrades

Im new to android development and I have a question about selling in the google android market. How do you sell upgrades to customers? For example if I had a free app that I would only allow the app to run for x number of minutes before updating and then have a paid version that would not have the limit. Do I have to have to publish 2 versions of the app or is there a way wit开发者_如何学编程hin the app to allow them to "unlock" the app? What about premium content like extra features? Thanks!

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To achieve what you're describing, you can also use in-app billing. After the trial period, you can popup a message saying the trial is over and asking the user to pay to continue using it. More info on in-app billing here: http://developer.android.com/guide/market/billing/index.html

Of course, another option would be to have 2 different versions (with 2 package names) - one for the trial and one for the paid version.