I am looking for an XMPP client that would continue to stay connected to the server when even when the app is closed on the iphone.  I am an IT admin, and my the solution I am looking for is this:  Does OneTeam keep an active connection on the iphone when closed/minimized, so that end-users on my company’s network would be able to send me an IM’s on my phone?

You cannot keep application running on the iPhone. This is a limitation of the platform itself.
However, OneTeam will support Apple Push on iPhone firmware 3.0, which will allow you to get notified when you receive messages even if your application is closed.