Send Free SMS from your iPhone, even international SMS.

http://sms.dynadel.com/

Chat across leading IM services AIM, MSN, Yahoo, and Google Talk, through a single chat window.

Mundu IM iPhone Edition:

Interoperable with the 4 leading IM services providers: MSN, Yahoo, AIM and Gtalk.

• Completely customized for the iPhone: the closest IM experience that replicates a native iPhone application
• Conduct simultaneous chat session with easy notification
• Scroll to see entire chat session (using the iPhone strengths)
• Add buddy like you would on a desktop messenger

http://iphone.mundu.com

M+ for Skype is a web service that enables voice and text communication with other Skype users and provides cost-effective calling to landlines and mobiles. Pure SkypeOut quality with no extra voice delays. The application is designed especially for iPhone’s touch screen and complements the design and interface of iPhone.http://skypeforiphone.com

AIM on iPhone, wrapped up in Joe Hewitt’s iUi.

http://www.tybyim.com

Post note and check for new tweets from your active life. “View New” feature only downloads new tweets to save massive loading time over the slow EDGE network. Operate one-handed with easer. If you are like us, you’re usually juggling more than just your tweets. We’ve made this interface simple but effective, and we hope you enjoy it as much as we do!

http://itweet.net

iPhone Chat Client is another AIM portal for your iPhone.

https://www.iphonechatclient.com/login.php#_buddies

FlickIM is a GREAT looking AIM client for your iPhone.

http://www.flickim.com/

A multi-user chat room application optimized for the iPhone.

http://www.zipbbs.com/

Beejive is a GREAT app which runs quick and allows you to connect to AIM, MSN, Yahoo, Google Talk, ICQ, and Jabber from your iPhone.

http://iphone.beejive.com

Sign in to AIM, MSN and ICQ using heysan! on your iPhone. Yahoo and GTalk support coming soon!

http://m.heysan.com/