1. IM+ Instant Messenger– It supports almost all popular IM services- Facebook, Google Talk, Live Messenger, Yahoo!, ICQ etc. You can add more IM services via in-app purchase. With IM+ Instant Messenger, you can send text messages, voice notes, images and videos. It supports multiple accounts and lets you customize the look and feel of the app.
2. eBuddy Messenger– One of the most popular free IM app for iPhone. It supports Google Talk, Facebook Chat, Yahoo Messanger, AIM, Windows Live Messenger, MySpace ICQ and Hyves. It lets you easily switch between chats.
3. imo instant messenger– It supports Google Talk, Skype, MSN, ICQ/AIM, Yahoo, Facebook, Myspace, Jabber, Hyves, VKontakte & Steam. imo instant messenger has all the features you can expect from a full-featured IM app for your iPhone, such as- push notifications, group chat, photo & video sending, searchable chat history etc.
4. Trillian– If you’re using Trillian, this is for you. This is the official Trillian app for iPhone that lets you access all the Trillian features on your iPhone. With Trillian, you can chat with your friends on G Talk, Yahoo, AIM, MSN, Facebook, ICQ and Jabber.
5. Skype– The official Skype app lets you stay connected with your friends and family with instant messages and free voice and video calls.
6. Kik Messenger– It lets you send messages, photos, videos & sketches instantly and easily with your friends. Kik has many useful features and very simple user interface.
7. Windows Live Messenger– This official Windows Live Messenger app for iPhone lets your send messages and more with your MSN/Windows Live friends.
8. Beejive for Facebook – If you’re looking for a good standalone Facebook chat app, use Beejive for Facebook. This is an unofficial Facebook chat app that allows you to chat with your Facebook friends on your iPhone and it is available for free.
9. WeChat– This is a cross-plateform instant messaging app that supports text, free hd video calls, voice notes, photos, videos, location data etc.
10. Nimbuzz Messenger– Another cross-plateform IM app that is available for free. With Nimbuzz Messenger, you can send instant messeges(Google Talk, Yahoo Messenger, Windows Live Messenger and Facebook), make voice & video calls and share files with your friends.