Does buying an Apple Watch require a separate cellular line?

This is the list of carriers that support the Apple Watch.

Apple Watch - Carriers - Apple

You an get a GPS Only Apple Watch, and the primary difference is that your iPhone has to be nearby, where nearby is somewhere in the same moderate wood frame constructed home, and of course when you leave the house, you take your iPhone with you.

An Activated cellular model shares the iPhone's phone number and for this service, one of the above cellular providers add a fee to your iPhone bill. In the U.S. the fee is generally about $10 U.S.

Things I do with my GPS Only Series 10 Apple Watch: • It tells time, date, day of the week • Every iPhone alarm, appears on my wrist, where you can acknowledge it, dismiss it, etc… • I like the iPhone 3rd party “Alarmed” app (http://yoctoville.com), for my alarms • Ring.com door bell can display a static image on the Apple Watch • Weather (this gets used a lot) • MyRadar 3rd party app will display radar image and send weather alerts • Rain Alarm 3rd party app will display a moving radar image • Make/Receive phone calls • Make/Receive FaceTime audio calls • Use Walkie-Talkie to other Apple Watches anywhere on the planet • Silence phone ringing by pressing the digital crown (great for SPAM calls) • Send & receive iMessages • Send & receive SMS TEXT • Say “Hey Siri, 14 and a half minute timer” • Say “Hey Siri, remind me when I get home to do xyz” • Say “Hey Siri, message my wife/husband/Susan/George/etc…” • Say “Hey Siri, start Outdoor Walk” • Say “Hey Siri, end workout” • Say "Hey Siri, find my iPhone" • Say "Hey Siri, flashlight" • Use a 3rd party garage door opener app and device (such as MyQ) • You can check your calendar • Read your email • If you need to take an iPhone picture where you cannot see the screen, use Apple Watch Camera app as a view finder/shutter release • Built-in Tides app, or you can get a 3rd party Ocean's Tide app for beach visits • Hand washing reminder and timer • Unlock your Mac (I do this several times a day) • Unlock your iPhone when you are wearing a mask • Track your exercise and physical activities Since my Wife got her Apple Watch, we have been able to reliably iMessage each other, as she never keeps here iPhone on her person. If my Apple Watch was lost, stolen, or broken, I would order a replacement as fast as possible, as I would miss it so much.