It seems from your question that you are talking about a separate email account for each iphone. In the users properties in AD are the new users enabled for active sync? You did not say whether you checked that. There is no default limit of two connections in exchange 2003, but you do need to make sure each account is enabled. I believe in Exchange 2003 all users are enabled by default, but that may not be true in your organization. In ours we disabled all users so we could control who connected and to make sure noone was connecting using a personal device. We then enabled those who had company owned devices and when new users are added to exchange they are disabled for active sync by our creation policies. They have to open a request to be enabled.