The Apple Watch Series 3 is available in two forms – one with cellular connectivity, and one with just GPS. For both, there's an all-new chipset inside as well as some key new features.
The main feature is the new built-in LTE cellular connectivity, offering voice and data communication and Apple Music streaming. The watch comes with an electronic SIM card and shares the same mobile number as the user's iPhone. Add-on plans start at $10/month from the four major US carriers.
As the replacement for the Apple Watch Series 2, this device is great for fitness and longevity, with run and cycle tracking on board and a water-resistant casing for swimmers, plus the heart rate monitor on the underside.  The Apple Watch Series 3 is running the latest watchOS 4, which has an updated Heart Rate app (including resting and recovery period monitoring), Workout app (with High Intensity Interval Training), as well as two-way data synchronization with GymKit-integrated cardio fitness equipment from companies such as Life Fitness, Technogym, Cybex, Schwinn, MS Artrix, Stair Master and Star Trac. The  Apple Watch Series 3 has a dual-core Apple S3 processor (which is 70% faster than the Apple S2). The cellular-capable watch has a red digital crown while the non-LTE version has a plain digital crown. It has a built-in NFC chip which can be used for Apple Pay. Apple claims 18 hours of battery life, which is a significant and useful upgrade. Despite the improvements to the software this latest Watch is rather expensive.
The Apple Watch Series 3 (GPS) requires an iPhone 5s or later with IOS 11 or later. The Apple Watch Series 3 (GPS + Cellular) requires an iPhone 6 or later with iOS 11 or later.

​Design/Look:
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Apple's build-up to the Watch's launch was all about the style. You have 3 Models to choose from, the aluminum Sport, stainless steel Watch and gold Watch Edition. They vary in price, although when switching to the steel Watch I found more people preferred the shiny exterior of the more expensive model, if your looking for a lighter watch, the Sport's anodized aluminum case and Ion-X glass make it slightly lighter. It's 30g instead of the steel's 50g, and gold's 69g. That adds up on my wrist when I'm wearing this thing for 18 hours a day before the battery life dies. Its aluminum frame matches the iPhone build and is therefore duller than the shiny stainless steel Apple Watch, but it still goes with a steel band just fine. The Ion-X glass substitute on the Sport model has proven resilient so far. I reviewed several "drop test" videos of shattered Apple Watch Sport glass, but more real-world tests would consist of minor wall and corner scrapes for wearables. Everything else is the same among all the models. The case sits 10.5mm off of the  wrist, slightly thicker than an Android Wear watch, but it has a stylishly curved glass and rounded off corners on the top, and a small bump to its black composite back's heart rate sensor.
It's reasonably thin for now, and its thickness does leave room for two large buttons, a classy sounding digital crown and a  side button,  Both are located on the right side for twisting and pressing through menus. A microphone and speaker are on the left side. The Apple Watch Series 3 comes with two bands in the box, a larger and shorter size in the same white/Black color. Changing the strap was incredibly simple. Overall, the design of the Apple Watch is slick looking and you can wear it for any occasion.

Is it the best cellular smartwatch:
Do you even need an Apple Watch in the first place? No, But, when I went to the gym with just the watch, it was pretty fun. And carrying around the Iphone at the gym can get very annoying. The Apple Watch Series 3 is the way to go. Be ready to pay for wireless headphones and $10 for service fee to have the full experience this watch offers.

​Pros:
  • Ability to ditch the iPhone
  • Water resistant 
  • Ease of making calls
  • Greater fitness focus than before
Cons:
  • Call issues if you are on captive Wi-Fi network
  • No international roaming
  • $10 service fee for celluar service

​Conclusion:

For iPhone users desperate for a smartwatch, an Apple Watch is perfect for you. Whether it's the Apple Watch Series 1 over the Apple Watch Series 3 will largely come down to what you want to pay. 
It relays some IOS apps and all notifications to my wrist without requiring me to constantly pull out and unlock my phone, and that's a nicely convenient thing to have. We've seen the Apple Watchs usefulness improve over time with new apps, software upgrades and stylish looks.  
It's a time-telling and time-saving convenience, though. That still requires a nearby iPhone and a hefty sum to buy. The Apple Watch price  will still raise plenty of eyebrows, that's why we recommend the cheapest aluminum Apple Watch Sport with another band for the moments when you need to look important.
The recommended Apple Watch Sport has the same dimensions, functionality and battery life as the other high end models. It's still a solid bet, now at a better price. When the Apple Watch Series 3 launched it really wasn't ready. Now several months later its a very different story. In many ways it works as an improved version of the already good Series 2. Offering this LTE  feature the Apple Watch in my opinion is still the best smartwatch on the market. ​ Check Amazon for pricing