A tablet is virtually the same thing as a smart phone yet there are some big differences. It's only $30/mo for 2G data transfer (more than enough), a month to month lease allows me to cancel service when not travelling, the screen is 10.5 inches and comes with a keyboard which enhances the ability to read and to communicate in long complete sentences vs. txt msg pckng on tny kybrd. Because of it's size, it functions better as a computer than a smartphone does and it's still light and somewhat compact.
I personally don't like trying to email, surf the web, skype, or play games on a smartphone - it's too small for my pork sausage sized fingers and makes it too hard to read with my much less than perfect vision.
During the ride, I'll have a small cheap phone (when I can get service), an old ipod for music and a camera that will take much better pictures than a smart phone.
Since I already owned everything but the tablet, this works out to be cheaper and better for me.
I hope that clears up your confusion.