iPhone 5 preview: Everything you need to know

We're now only a few days away from Apple's (Nasdaq: AAPL) iPhone 5 unveiling, which is set for this  Wednesday, US time.

The whole mobile world will be anxiously watching for what Apple has up its sleeve, and investors are already banking on a device no one has ever officially publicly laid eyes on to lift the company to new heights and decimate the competition.

The apple of Apple's eye
The iPhone is easily Apple's most important product family, generating half of trailing-12-month sales. No other product even comes close, and even the core Mac business has already taken a backseat to the iPad as a revenue driver.

Source: SEC filings. TTM = trailing-12-month. Figures may not add precisely due to rounding.

The relative softness in iPhone unit sales last quarter limited Apple's overall results since it's such a major contributor to the top line.

On top of that, reports estimated that Samsung's current flagship, the Google (Nasdaq: GOOG) Android-powered Galaxy S III, dethroned the iPhone 4S in August as the top-selling smartphone at most wireless carriers. As if that wasn't enough, both Nokia (NYSE: NOK) and Motorola have just recently unveiled new flagship devices, the Lumia 920 and Droid RAZR HD, respectively, so the competition continues to intensify.

Apple needs this
It is imperative for Apple to release a blockbuster device if it hopes to satiate investors' appetite for growth and fend off competition among high-end smartphones, particularly from the Android camp.

The Apple rumour mill never sleeps, and constantly churns out new tidbits to drive speculation. That means that potential buyers are well aware that a new model is coming and postpone purchases accordingly, but it also means that careful watchers already have a pretty good idea of what to expect.

Getting touchy-feely
For the first time in the iPhone's history, Apple will be increasing the screen size from a 3.5-inch display to a 4-inch display. While Android rivals continue to offer just about every screen size imaginable, some up to nearly 5-inch displays, Apple is playing this spec conservatively. In order to slim down the device, Apple is reportedly using in-cell display technology, which integrates the touch sensors directly into the LCD and eliminates the need for a separate layer. However, if it turns out consumers really do want something bigger, the iPhone 5 may disappoint.

This will also be the first iPhone to feature 4G LTE data speeds, again a requisite to stay abreast with the Android competition. One advantage Apple may be able to wield in this department is battery life, as most LTE devices are notoriously short-lived.

The physical case is also being redesigned and follows in the unibody footsteps that Apple has taken throughout other product families. This will yield benefits such as a sturdier casing and physical space efficiencies. Supply chain leaks show a two-toned design with what appears to be glass windows at the top and bottom to allow radio signals to pass through, since metal obstructs these transmissions.

After nine years, Apple will also move to a smaller proprietary dock connector, shaking up the third-party accessory market in the process.

When can I get my hands on it?
The US launch date is rumored to be Sept. 21, nine days after the unveiling. The launch happens to be when US carriers have scheduled vacation blackouts for employees, as they'll need all the able bodies they can get to handle the onslaught of rabid iPhone buyers.

Apple is always quick to launch devices very shortly after introduction, an attempt to minimize the Osborne effect of consumers delaying purchases waiting for the new models, although there's little it can do about the rumor mill we all know (and love) at this point.

Make no mistake: this product launch is Apple's most important for the entire year, since so much rides on the iPhone's success.