eBuddy Messenger (1.8 MB), a popular instant messaging service support multiple accounts including GTalk, Windows Live Messenger, Facebook, Yahoo, ICQ, AIM, MySpace and more. Useful settings include hiding offline buddies and blocking unknown users. Ad-supported.
WhatsApp Messenger (9.4 MB), chat with your friends and family using this messenger across multi types of devices including Android, iPhone, BlackBerry, Windows Phone and Nokia phones. You can send text, pictures, audio and video messages. This app is free for the first year.