MobileChat is a multi instant messenger for iPhone.

Changes:

Horizontal/Landscape Orientation Availability
“New IM” finally works
“Send” Button has been relocated to the keyboard (in place of return)
iPhone Firmware 1.1.3 Compatibility
DNS Issue that plagued 1.x and 2.0 has been resolved.
BSD Subsystem dependency should be gone.
Added support for XMPP
GTalk has been temporarily removed
Sign On progress notifications (as seen in screenshots)
Disconnect Notification: if you get kicked off, or you can’t sign on, you’ll be alerted now
Conversation code-base optimized

http://blog.twenty08.com/2008/02/25/mobilechat-v21-now-available/