When I preordered my Kindle Fire HD 8.9, I originally ordered the 4G model. I've always enjoyed the 3G E-Ink Kindles so I just assumed I'd want the 4G connectivity on the Fire HD. Meanwhile, I received a 7" Fire HD, which of course is Wi-Fi only.
After using the Wi-Fi Fire for a while, I realized my use patterns are different on the color tablet. I primarily use it for reading color magazines, non-fiction books with illustrations and photos, web, email, and sometimes listening to music. Work or play that requires Internet connectivity can wait until I'm at a Wi-Fi hotspot. When the details of the 4G data plans came out, even though the prices are reasonable, I felt that was lot of cash to tie up on one device.
Getting a 3G Kindle Paperwhite was a no-brainer, on the other hand, since the only cost is the $60 price difference on the initial purchase. There's no data plan or monthly payment- the 3G data access is for the life of the Paperwhite. While Amazon no longer allows unlimited web surfing over 3G as they did on the Kindle Keyboard, the 3G connection is still very useful. Not only can you shop for more reading material, you can also use Wikipedia freely. And Amazon keeps your current place, as well as all your bookmarks, highlights, and notes, synchronized in all your Kindle books on all your Kindles and Kindle reading apps.
Enter the smartphone. As the date when I could get a discounted phone upgrade approached, I became aware that virtually all smartphones can act as mobile hotspots, providing Wi-Fi Internet to several devices. Also, data plans are now tiered for different data amounts per month and shared with other phones on a family plan. So I got one.
Now I can connect to the Internet just about anywhere while traveling. Of course, for email and minor web surfing I just use the phone. But when I'm sitting down to do some work, I can connect the Fire, the Paperwhite, and my laptop to the net at the same time. It seems to work very well. The only catches are that the phone uses a lot of power when acting as a Wi-Fi hotspot, so you really need to keep it on the charger. Also, you can't make or take calls. But that's why Alexander Graham Bell invented voicemail.