The iPad's lack of a built-in camera is not stopping a number of enterprising developers from coming up with ingenious solutions that allow users to share their iPhone cameras instead.
These systems usually come in the form of a pair of apps: you install one on the iPhone to capture images from the camera, and the other on the iPad to view and manipulate the images.
The Camera-A and Camera-B apps, written by indie developer Yusuke Sekikawa, make up one such combo. Camera-A is installed on the iPad and connects to Camera-B, which runs on the iPhone, either via Wi-Fi or using iPhone OS's peer-to-peer Bluetooth connectivity. The set up process is easy and intuitive (essentially, all you need to do is make sure that both apps are running) and the video feed, while at times grainy and less than fluid, is perfectly serviceable. Camera-A/B's major shortcoming is the interface, which is somewhat spartan—all it allows you to do is take snapshot of the video feed, and it’s pretty unintuitive.
Another entrant in this category is the freshly-released Camera for iPad, which, unlike Camera-A/B, comes in the form a Universal application that can be installed on both an iPad and either an iPhone 3G or 3GS. Unlike its competitor, Camera for iPad only supports Bluetooth connectivity, which limits its range somewhat; however, it features a somewhat slicker interface—although taking a shot from the stream is still all you can do with it.
Beyond the immediate novelty, the functionality provided by both these applications is severely limited. The quality of the images that’s transmitted across the stream is not as good as what you would be able to capture on the iPhone, where you also have more tools at your disposal to manipulate it. However, both Camera-A/B and Camera for iPad provide an excellent example of what’s possible with the combination of an iPhone and iPad; it's not inconceivable to expect that this kind of functionality will become part of applications that will put it to better use, such as chat and instant messaging apps.
Camera-A and Camera-B are both available from the App Store; the former costs $1 and requires an iPad running iPhone OS 3.2 or higher, while the latter is free and works on iPhone 3GS devices running iPhone 3.1.3 or higher. Camera for iPad, which can also be had for $1, is a Universal application compatible with either an iPad running iPhone OS 3.2 or higher or an iPhone 3G or 3GS running iPhone OS 3.1.3 or higher (the App Store page also claims that the app is compatible with the iPod touch, but that's clearly an oversight, as that device lacks a camera).