A few weeks ago I bought an "Epic 4G" phone from Sprint. This is one of the Samsung Galaxy S variants. It has a custom GUI called "TouchWiz" made to look more like the iphone and is loaded with Sprint applications including a game demo, nascar related and football related applications that are installed as "system applications" and cannot be removed by the user.
It also has a Sprint replacement for the wifi hotspot tethering so the user is required to pay $30/mo for that feature that is normally native to Android even when they're already paying for an unlimited data plan.
It has sprint logos and music that plays on startup and shutdown that cannot be removed without rooting the phone.
A recent update added a media portal where the user can purchase movies and tv shows from Sprint partners. Also a "system app" that cannot be uninstalled.