iPhone 4 is now available, and thousands are lining up to get their hands on one. With pre-order sales already crushing the records of previous iPhone models, if you've been thinking about buying a new phone, or upgrading your current iPhone, we have ten reasons why you should.

FaceTime:

FaceTime, the new video calling feature Apple showed off at the iPhone 4's unveiling, is one reason many believe the iPhone 4's sales have been so strong since the device became available for pre-order on June 15th. The addition to the phone of a front-facing camera makes video calling as easy a making a normal voice call, with no setup required, and everything needed built directly into the call controls of the phone. Apple, however, didn't stop there. Users can tap an icon on the screen, and use the camera on the back of the phone to show the person they're calling what they are seeing as well. The video calling feature also targets the hearing imapaired, creating a portable solution for staying in touch that doesn't require voice communication, as shown in Apple's iPhone 4 video featuring two poeple using FaceTime to talk to each other using sign language. Although FaceTime is only supported over Wi-Fi for now, and only works between users of the iPhone 4, with sales as brisk as they have been, it probably won't be a problem finding people you know to make a video call with.

720p HD Video Recording:

The addition of a video camera to the iPhone 3GS was a feature welcomed by iPhone users everywhere. With video recording now updated to be able to handle 720p HD, the possibilities for recording and sharing video just got a whole lot better. The LED flash can be used in situations where low light is a problem, and Apple's new iMovie app for the iPhone will make editing videos you record an easy task. Manufactures of pocket video cameras should be worried, as many iPhone users will choose to leave their standalone pocket video cameras behind, opting for the convenience of convergence instead.

5-megapixel camera with LED Flash:

In addition to the new HD video recording capabilities of the iPhone 4, the still picture camera has also gotten an upgrade. The rear camera on the new device is now 5-megapixels, features a built-in LED Flash, and has a 5x digital zoom. Pictures will now be sharper and clearer than those taken with previous versions of the iPhone camera, making it more convenient for users to leave their pocket cameras at home, knowing that they can still take a good quality casual photo when the need arises.

Retina Display:

The 3.5 inch Retina display, at 960 x 640 pixels with 326 pixels per inch, makes for sharper, smoother, more realistic looking text, images, and video. Jagged edges around text, even when zoomed in, have all but disappeared, with text appearing more like it does on a printed page. The display should make reading Web pages, books, and other documents easier on the eyes. Photos and videos will also look better, with colors that are more vibrant. Though the improvement of a display may not seem like a big deal to some, users do spend most of their time looking at the phone's display. Therefore, any major improvements in this area can only help with making the iPhone 4 more comfortable and enjoyable to use.

Apple's A4 Processor:

Apple is using its new A4 processor in the new iPhone 4, the same processor which has received much acclaim in the iPad. With the A4 processor, the iPhone 4 receives a considerable performance boost, one that makes playing games, watching videos, and switching between apps smoother and faster than before. The processor has also been designed to work seamlessly with the phone's other hardware and software, which also contributes to better overall performance.

Better Battery:

Battery issues are always a problem with today's latest phones. With users doing more on their phones than ever before, a phone's battery can quickly become drained if not careful. Apple has always stated that battery life is important to them, and they have shown that by consistenly improving the battery life in many of their products, including laptops, iPods, iPhones, and the iPad. With iPhone 4, users can expect improved battery life once again, with 7 hours of talk time on 3G networks, up to 10 hours of web browsing on Wi-Fi (6 hours on 3G), up to 10 hours of video playback, and up to 40 hours of audio playback. With numbers like those, users should have no problem getting through a full day of use without having to recharge. The iPad has already been praised for its better than expected battery life. No doubt the iPhone 4 will as well.

Antenna Placement:

Many users have reported problems with dropped calls and weak signals since the first iPhone was introduced. The problem has been mostly blamed on AT&T's heavily burdened network, but the new placement of the iPhone 4's antennas should help to improve call quality in most cases. The metal band surrounding the phone not only serves as the phone's support structure, but contains the phone's antenna system. Placing the antennas on the outside of the phone is a good move by Apple, hoping to improve on the call quality criticisms they have had to endure in the past. Users in areas with high concentrations of iPhone users, or spotty coverage by AT&T, may still experience some problems, but many will notice an improvement in call quality overall. AT&T has also stated that it plans to have network improvements in place by the end of the summer, so that should help call quality as well if they remain on schedule.

(Update 6/25/2010: Some users have reported that when holding the iPhone 4 in their left hand, if their skin touches the small, black line that runs across the metal band the signal bars indicating the strength of their signal begins to drop after a minute or two. Reports from other users, however, state that they haven't had any problems with this particular issue at all. Overall, improved call quality and signal strength have been reported by most users, when the touching of the antenna issue that has surfaced isn't brought into play. If you normally hold your phone in your right hand, you probably won't have any problems. For those experiencing problems with fading signal strength, using a protective case, or one of the new rubber bumpers Apple sells for the iPhone 4, should solve the problem. The issue seems to only happen when a person's skin directly contacts the lower left edge of the metal band surrounding the phone. A case or bumper will prevent that direct contact.)

iOS 4:

Apple's release of iOS 4 has brought many new features to the iPhone, making users of previous iPhone software happy to see the improvements. From multitasking, to app organization via Folders, to e-mail improvements, and more, the new iOS 4 makes using the iPhone as easy as ever, and lets users be more productive at the same time. Though iOS 4 is supported by the iPhone 3GS, iPhone 4 is designed to take full advantage of the more than 100 new features introduced with this latest release. Users of previous iPhone software, as well as new users, should enjoy iOS 4's ease of use, which has always been one of the iPhone's best features.

Current iPhone Doesn't Support iOS 4 Features:

We've talked about some of the new features iPhone 4 has to offer over previous models, and all are good reasons to buy the new device. Another good reason is if you own an older iPhone model that doesn't support all of the features of the new iOS software iPhone runs on. iPhone 3GS has the hardware built-in to support all of the features of the new iOS, but iPhone 3G users will find some features will not function with their current phone, and first generation iPhone users will not be able to use iOS 4 at all. If you fall into this category, then you might want to consider upgrading your current iPhone to the iPhone 4, in order to take advantage of all of the improvements that have been made.

Buying Your First Smartphone:

Just as users of older model iPhones should consider upgrading to iPhone 4, to take full advantage of the new hardware and all the features iOS 4 has to offer, if you are new to buying a smartphone, the iPhone 4 is a great choice as well. If you already use iTunes, have an iPod, or other Apple product, even better, though you don't need to be an Apple computer user at all, or an iPod user, to use an iPhone.

From the first iPhone to the latest iPhone 4, the device has always received high marks for its ease of use and all of the many features packed into its small design. The iPhone is like having a small computer in your pocket, and its pros definitely outweigh its cons. With so many apps in the App Store, the ability to view the Web and have pages appear as they do on a normal computer screen (regardless of whether the browser supports Flash or not), the ease of managing your e-mail accounts and calendars, the ability to take photos and shoot HD video, and now the ability to make video calls to anyone, anywhere in the world, the iPhone 4 does it all. Whether for casual use, business use, or a mixture of both, the device allows you to set it up however you like. Put your photos, videos, and music on it. Put the apps that will be most useful, and enjoyable, to you on it. The iPhone can be customized to work the way you want it to, which is one of its best features, perhaps even its strongest feature. Sure there are plenty of good smartphones on the market, but for convenience, ease of use, and access to the widest variety of apps around, you can't go wrong with the iPhone 4. Try one out. I think you'll be pleasantly surprised.

iPhone 4 comes in black and in white, with the 16GB model selling for $199 and the 32GB model selling for $299 with a new two-year contract from AT&T. Current iPhone users looking to upgrade to iPhone 4 can view their upgrade eligibility status by visiting www.att.com/wireless/iphone/, or dialing *NEW# on your phone.