Yes, RingPlus plans will work with your unlocked Sprint device. RingPlus runs off the Sprint network so there should be no problems
Click here to Compare RingPlus Plans
When you purchase the plan through RingPlus they will send you a SIM card. Make sure you select the correct SIM size, wait for it in the mail and then simply plug it into your HTC EVO
Now, when switching carriers, it is always good to know what other options you have on the market. With the Sprint device being unlocked, you have a lot of available service options that I would consider checking out before making a final decision.
Click here to Compare all BYO Sprint options
From those search results, here is a list of carriers compatible with your device that might be beneficial to you! These carriers also run off the Sprint network and offer great data plans, low monthly cost and awesome call/text quality!
TIP If you currently have cellphone service then make sure that you don't cancel your existing plan until you have ported your number to the new carrier - this is usually part of the sim activation process with the new carrier. Most number ports are done inside an hour (sometimes less)