Yes, as a developer, Apple's SDK does allow applications created with it, to interface with almost every application of iPhone OSX, as well as the built-in API's,
for example, the image picker. As stated above these applications run in a sand-boxed environment which essentially means applications have no access to
another applications data. Interfacing is carried out by the use of links or commands which trigger built-in APIs. For example, an address in a location-based
application could link to the Maps.app and GPS module, but actually retrieving the data and placing it back into the location-based application is prohibited.
Lets not forget, even though Apple says they opened up the 'same' APIs and tools they use when developing for the touch platform, they did, in a way,
but Apple don't have the tedious restrictions.
The public SDK rules don't apply to Apple internally. Likewise, Apple's applications are not 'sand-boxed' in thier own environment for security, there is no need
for them to be. Any applications we'll see from Apple will not follow the SDK rules, because for Apple, there aren't any rules, apart from the obvious privacy
policies which must be obeyed. This and this alone will make Apple developed applications 100 times better at data management and other related tasks,
than the public SDK created applications.
After saying this, I cannot wait to see the sheer explosion of applications and genre of application the App Store (both Apple/Developer designed) will bring to
iPhone and iPod touch in the up-coming 2.0 software update.
R-Fly