To open a map (in map application or browser) you need to use an Android "intent" to "VIEW" the specific URL. This facility requires the "webintent" plugin for Android (http://borismus.com/android-phonegap-plugins/).
The source is available: https://github.com/phonegap/phonegap-plugins/tree/master/Android/. Documentation on using it with PhoneGap is https://github.com/phonegap/phonegap-plugins/blob/master/Android/WebIntent/README.md.
This sample PhoneGap (0.9.4) project includes an example of using the webintent plugin to open the built-in map browser: PhoneGapIntents.zip
The scanner used is the standard ZXing barcode scanner: http://code.google.com/p/zxing/. This is supported by the "barcodeScanner" plugin.
The source is also available: https://github.com/phonegap/phonegap-plugins/tree/master/Android/. Documentation on using it with PhoneGap is https://github.com/phonegap/phonegap-plugins/blob/master/Android/BarcodeScanner/README.md.
This sample PhoneGap (0.9.4) project also includes an example of using the barcodeScanner plugin from a PhoneGap application: PhoneGapIntents.zip
If you have problems installing the barcode scanner application (e.g. web proxy problems) then you can install it over the USB debugging connection from the local computer using the "adb" command, in particular "adb install <appfile>": see http://developer.android.com/guide/developing/tools/adb.html. The adb command can be found (in C11) in C:\Program Files\Android\android-sdk-windows\platform-tools\ or C:\G54UBI\AppInventor\commands-for-Appinventor.