Unless they offer Exchange email hosting, no. However if you can setup a rule to forward all your emails to Gmail you could use Gmail’s Exchange protocol support. If you are in control of the hosting I’d recommend just switching to Google Apps (it’s free if you can find the right link). Be warned though the iPhone only supports push via one Exchange account so you can have a personal and business account both getting push (although maybe you can with MobileMe + Exchange). Hope that helps!