The app ID for a native mobile app, on the Android and iOS platform, is the unique key binding the actual app, installed on the end-users device, to the update mechanism in Apple App Store and Android Market.

This is exactly why the app ID is important, to the road ahead for your Mobile App strategy. This app ID will be the key to all future updates of the app, whatever future development cycles, new features or brand changes you app will go through.
Let’s say you are 6 months down the road, and have 100.000+ active installs on end-user devices, and you have to change your app completely. The change could be anything; re-coding, re-branding, re-design, feature changes etc., if you want your current 100.000+ end-users to receive the new version of the app, your app ID have to be the same, otherwise they wont get update notification in Apple App Store or Android Market.

Here is an example of an app ID:
com.brandname.appname

Your strategy might have multiple apps, standing side by side – but that still make the app ID important, to each individual app.

Let take for example Twitter, their app ID is: com.twitter.android, if they haven’t thought of a generic future proof ID and had to change this. They would have to re-market the new app, to all their current users, about uninstalling the current app and re-download the new app. All this because each app ID is treated as an unique product in Apple App Store and Android Market.

Take a look at the FourSquare app for Android as an other example. The app ID is com.joelapenna.foursquared, so who is Joe LaPenna? And what is his relation to FourSquare? Did he even work for them? No, he works for Google on their Latitude team… (get the story here). But I guess you get the point, FourSquare is currently stuck with an old app ID.

So you might think; whatever, that’s no big deal! If it works for FourSquare, I don’t care! But as a side node, I can mention that the name is visible, in the URL for your app in Android Market: https://market.android.com/details?id=com.joelapenna.foursquared

This whole app ID factor is mostly important to remember, specially if you outsource the development of your native app(s) to a subcontracting developer or company. Some subcontracting developers or companies, tend to put their own name, into the app ID, e.g.: com.subcontractorname.apps.yourappname

So my advice is always: treat you app ID as company brand- or domain-name! Be in control, make sure is generic and future proof! …even though I know it might be a geeky technical detail

This might spare you in the future from “closing down” an app, you already have in the market. To launch and re-market your new app, and possibly loose a huge amount of end-users, who would be stuck with the old version. Who haven’t tried this already…!

Note: App ID are also called Bundle ID in the App Store or package name on Android.