There's not a whole lot to say about the HTC EVO Design 4G when it comes to messaging. The built-in Messages app does a fine job of displaying conversations in a threaded view and offers plenty of MMS options for attaching pictures, video, audio, location, vCard contacts or vCalendar appointments.
HTC's Peep is included, which is the company's own take on Twitter; it's a perfectly workable app and to be honest, we have yet to find Android's greatest Twitter app (third-party Tweetcaster Pro comes close), so you could do much worse.
Friend Stream is also preinstalled, which duplicates most of the same Twitter functionality but blends Facebook and Flickr into the social fun. Our preference has always been to download specific apps for such services from the Android Market – er, Play Store – but less savvy buyers will be happy to have these built-in.