Rumor Mill

I know the standard answer is to throw out the hardware features of the phone, and how it's not a 4G charge... and the reality is that neither of those answers are going to suffice for techncially savvy people that know most of the phone's features will still work without a Sprint account.

This is my speculation.

The Evo is the first 3G and 4G phone. Everyone here knows that. Everyone also knows 4G isn't everywhere yet. I think the $10 fee is to help offset the cost of both the higher 3G data usage for each Evo (think Qik, YouTube HD, Hulu and Flash enabled sites), whilst enabling Sprint to further build out the new 4G network.

Also realize that the Evo's plan does include unlimited 3G (as does every Everything Data 450 or higher plan, I know), and with the unlimited hotspot, it's currently the only non-grandfathered way to get unlimited 3G.

So look at it these two ways:

If you're opting to use mobile hotspot and have a cellphone, you're effectively paying only $39.99 (the 29.99 hotspot + 10 evo fee to have unlimited 3G and unlimited 4G.

If you're not opting to use mobile hotspot and don't have 4G, you're using a phone that is capable of downloading and using many more Internet resources (that require more bandwidth), which will most likely actually use that bandwidth, and even not, you're helping to speed the deployment of 4G in your area.

If you have 4G, lucky you, have fun.

I wish Sprint would give us reps better answers, and customers as well... but that's my speculative response, and I hope that works well enough for you all.