One year ago I developed a sync adapter for Android. At that time it wasn't possible to show a custom activity or to customize the standard activity to edit a contact. The result was that, although it was possible to configure the synch adapter in a such a way that the added contacts where editable, to edit a contact was not really feasible, unless the custom contacts were the same as the normal ones.
Is it still like that? Did google fix the problem?
See for a reference: http://groups.google.com/group/android-developers/msg/86d4d895e88a5ebb
I found this: http://groups.google.com/group/android-developers/msg/85f9304dfcc4e284
but it does not say where to find the documentation