You will see the numbers on your phone simply because the image is analyzed and the computer is able to figure out where the number should show up on the phone based on the phones accelerometer and an AR (augmented reality) tool called hieroglyphs. It is difficult to interpret an object without any reference. A hieroglyphic is an image that acts as the reference. There are already some android apps that utilize hieroglyphs; namely AndAR Model Viewer. The video demonstrates AndAR in action. The point is that instead of projecting a chair or other object, a keypad would be displayed. The 0-9 keypad, a-z keyboard, or other specialty buttons would no longer be constrained to the size limitations of the phone. They would no longer pose a physical requirement on the phone. This all assumes you still want that info linked to the location of the phone. It may as well just be a designated area within your field of view.
Bluetooth resolves several of the constraints. There is no need for a port for the headset jack. There are Bluetooth enabled headphones. Video and audio can be transmitted and received similarly. There is no need to run a cord from your phone to the glasses when it can all be transmitted wirelessly.
A camera? To take full advantage of your new, fully customizable, AR environment at least one camera would be built into the headset. You don't like the user interface of reality, then program a different one. The head mounted display would render a phone's camera redundant. Do not worry. Your eyes will not be strained by staring at a screen because eReader type displays will be used. That technology still has to improve refresh rates and coloring to meet streaming video demands. It is improving rapidly. My guess is that in 2 years it will begin to meet these needs.
Volume control would be virtual.
The power button would be virtual.
HDMI transmission is achieved with Bluetooth.
Charging can take place using inductive technology. Simply place your phone on a mat. No port is required. PowerMat is likely the biggest name in this market currently. I would have put their product instead of their logo, but really, while the technology is great, a phone sitting on a mat is just boring.
I cannot say the same about the SIM card; the card some phone companies use to identify their customers. Barring the companies switch to different methods, it would have to reside some place on your person. However, it could still be integrated into the headset or auxiliary device.
What is left? A brick. Since many of the components have been removed, the battery and processors can stretch out with much more leg room. It has become a slab of fully enclosed plastic and metal that is impervious to the elements. Dropped your phone on the ground. No worries, the slab phone can be dropped 10 times further without damage. Ever dropped your phone in the toilet. No worries, disgusting, but no worries. Your new slab phone can be water tight depending on the options. Want a warranty; you get it for $1 cause the carrier knows it would take acid or nuclear radiation to destroy that beast. And if it did the warranty would not cover it. Some things never change.
All of these will be features available based on the phone model. The only technology that is needed is the eReader screen to avoid eye strain which I said would likely be ready for market in 2 years. That makes it perfect timing for Google to unveil their design as a prototype stage. They will work on their product and it may find some people interested in wearing it for short term periods. By the time all the bugs are worked out the only thing left to do will be to switch out the screens. It is a classic example of how Moore's law is being used to bring products to market.
As this is my last post on the topic, here is a video from a Mashable post that shows some progression in their work just within the past month. A month ago, Sergey Brin, a Google co-founder, discussed the project briefly with Robert Scoble (@scobleizer on Twitter) Whether true or not, it was said or joked that the glasses at the time only continually rebooted.