You have two options:Is it relatively easy to tether an android smartphone to the chromebook? I have a galaxy s phone with unlimited data plan and was hoping to tether instead of buying the 3g chromebook.
Your first option is to add T-Mobile's Wi-Fi tethering plan to your account, which is an extra $15/mo. Your second option, which is what I did (I have a Galaxy S 4G), is to root your phone and install an app that allows Wi-Fi tethering with root access. I had no clue what I was doing when I rooted my phone, but it turned out to be a lot simpler than I expected.
I assumed you are with T-Mobile. That in mind, know that T-Mobile has a data cap of 5 gigabits. Fortunately they don't charge extra for going over, but they will switch you from 4G to Edge (aka 2G) for the remainder of that billing cycle if you do happen to cap out.