If you simply want to experience the look and feel of that era:

If you want to use your vintage HTC phone (such as the HTC Touch Pro, HTC Diamond, or HTC TyTN II) for communication, you must rely on protocols that do not require modern server-side application handshakes. 1. IRC (Internet Relay Chat)

Connect your HTC phone to a PC via a USB cable (using Windows Mobile Device Center or an SD card reader) and drop the .cab file into the phone's internal storage.