SAN FRANCISCO – To some people, Apple’s new iPhone 4S isn’t the overhaul they have been hoping for. Its model number, which doesn’t include a “5,” stinks of the status quo.

That’s ridiculous.

Sure, the 4S doesn’t render the iPhone 4 obsolete, and on the surface they’re nearly identical. But with a faster processor, new software, a voice-activated personal assistant and a souped-up camera, it’s a major improvement.

The 4S will be available Friday in black or white. It will cost $199 to $399, depending on storage space. It requires a two-year service contract with Verizon Wireless, Sprint or AT&T.

If you have an iPhone 4, you may want to hold on to it for now. But if you’re sporting an older model such as the 3GS or considering making the leap to an iPhone from another type of handset, it’s an excellent excuse to buy one.

The coolest new feature on the 4S is Siri, a software-based personal assistant who responds to your voice in a somewhat robotic, yet soothing female tone.

Siri can do all sorts of things, from setting your alarm clock to finding a good local sushi joint to playing DJ with your music. She can’t bring up websites, but she can search the Web for pretty much anything.

Once you let her know who you are and where you live, she can even do complex tasks such as reminding you to call your boyfriend when you get home, helped by the phone’s location technologies such as GPS. She can understand conversational English, which is great because I was able to speak as I normally would (though I did have to enunciate well). This means you can say things like, “what’s happening today?” or “what’s going on today?” and she’ll let you know what’s on your calendar.

She’s also a dictation dynamo, transcribing emails and texts much better than a phone running Google Inc.’s Android software. It would be awesome if she could intelligently insert punctuation marks, but she does get them if you tell her “period” or “exclamation point.”

For a particularly difficult test, I read a random paragraph from a copy of “The New Yorker” to the 4S and to an Android smartphone. Siri didn’t get all the words correct, but she overwhelmingly beat the competition.

Of course, after spending all this time together, I wanted to know all about Siri. I asked her a bunch of personal questions, with mixed results. Her favorite color is something she doesn’t know how to say – “sort of greenish, but with more dimensions.” She changed the subject when I asked if she was seeing anyone.

Note for foul-language fans: Siri understands profanities, but she may chastise you. She did this to me, so I asked whether she had a problem with my language. She told me to get back to work. I apologized.

Beyond Siri, I was happy to see a better camera on the 4S, which has an 8-megapixel lens compared with 5 megapixels on the iPhone 4. My shots had sharper details as a result. The new camera can also take pictures faster, and a new lens gathers more light so pictures shot in dim lighting look better.

The addition of a camera icon on the phone’s lock screen makes it easier to start snapping. Just double tap on the “home” button when the phone is asleep to bring up the icon, and tap that to open up the camera. Also, there’s finally a physical camera button on the iPhone as the 4S’s volume-up button does double duty.

You can even record high-definition videos in 1080p on the 4S – the best resolution currently available on a consumer camera.

The iPhone 4S has the latest version of Apple’s mobile software, iOS 5, which seems geared toward making the phone even easier to use.

One of the best additions to iOS 5 is iMessage, which lets you send texts, photos or videos to other Apple devices over Wi-Fi or your wireless carrier’s data network. That makes it easier to send texts to iPads and other devices that aren’t phones. It also saves you texts, if you’re not on an unlimited text plan.

With the iOS 5 upgrade, swiping the top of the screen now brings up a handy notification page, which shows you things such as appointments, reminders, weather and stock quotes.

IOS 5 also gets points for allowing you to step away from your computer: You can set up your iPhone and receive software updates on the device itself, without plugging it in.

In addition, it includes Apple’s new iCloud content-syncing software, which can store your content online and push it wirelessly to your devices. If you buy lots of digital content from Apple, you’ll like how it can automatically add songs, apps and e-books from Apple’s iBookstore to all your iCloud-connected devices. Unfortunately, it doesn’t do this with TV shows or movies, so you’ll have to go into iTunes on the device to download them or sync the content from a computer.

The iPhone 4S’s performance is noticeably bumped up by a new dual-core A5 chip, which is the same processor in the latest iPad. With this chip, the phone can process graphics and complete other tasks much faster. Web pages, especially graphics-heavy ones, loaded faster than they do on the iPhone 4

Call quality was decent over Verizon Wireless’ network, though it sounded a bit flat. Calls are supposed to be improved on the 4S with the inclusion of two antennas that the phone can use to receive or send data.

With location services on and using a combination of Wi-Fi and 3G cellular service, I got about six hours of copious texting, websurfing, video-watching and calling out of the 4S before the battery needed recharging. Given this, it should hold up fine during a day of normal use.

If you have an iPhone but don’t want to trade up to the 4S, you’re not entirely left out: iOS 5, which includes iCloud, will be available Wednesday as a free update for the iPhone 4 and 3GS, both iPad models and later versions of the iPod Touch.

If you don’t have an iPhone, however, the 4S is a great one to get, even if its name doesn’t include a “5.”

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