I have used it. Its not the best app but it gets the job done. I can't wait till Apple releases an iChat app. I love the iPhone, but I thought Apple would of released applications quicker then what they have.
I can't find an app that does what I need so I end up having to use two differecnt apps. First I use MobileChat, cause I want to have a native app running. My only real complaint with MobileChat is that it doesn't remember my user name and password if I get logged out. For a second from and my other AIM id I use Jivetalk http://iPhone.beejive.com I would love to see this as a native app, as it so far is my favorite IM web based client. I really want to like ApolloIM but I can't keep it connected like MobileChat and Jivetalk. Almost every time I pick my phone up to check and see if I got messages, I see the disconnected warning with Apollo. I know all apps are a work in progress, and I can't wait to see a nice and easy to use Apple IM app, but for now, I guess having to use two apps is what I got to do
"There’s no shortage of instant-messaging options billed as ideal for the iPhone, but up until now unless you’ve wanted to pay AT&T for an SMS message each way then you’ve been forced to use a web-based client. Now, though, there’s a very early beta of the iPhone’s first native IM client, Apollo IM, to be excited about."