First of all, the iPhone is a great device. The thing works as advertised. Having used two other smartphones in the last couple of years, it clearly is the best when it comes to interfacing with the device. It seems to have an uncanny way of just knowing what you want to do.
The Mac philosophy is clearly in play here. Whereas Windows often makes people cower into corners because it presents a "press this button and every thing will go wrong" interface, the iPhone invites touching. See a button, go ahead and press it. It's there for you to use. Come out of your shelters people, it's safe to compute again!
Although the EDGE network that AT&T uses is not the quickest for browsing, having just come back from a business trip in Ft. Lauderdale, I was impressed with how many places I could use the available Wi-Fi (and free at that) and speed things up. Call quality was excellent. And the ability to dynamically enlarge text in emails and in the browser was phenomenal. This feature alone bypasses the typical compromises that other handset makers have when you have a system wide font setting with only 3 sizes, too small, small, and cyclop-sized.
If your church uses Microsoft Exchange as your email server, you will have to turn on the IMAP email protocol and open up a port in your firewall to allow the email traffic through. Some administrators may not like that because of security concerns but I hope to see a resolution to that soon.
Otherwise, most email setups should work just fine for your iPhone. The ability to stay connected when you're physically disconnected is an awesome and liberating feeling. No need to carry a laptop everywhere you go just because you need email and browser connectivity. Not to mention that it feels not much bigger or heavier than my previous Motorola RAZR V3 so I carry it often just in my pants pocket, leaving the belt clip behind.
The iPhone isn't perfect but it's better than all the other devices I have worked with and with the impending software development kit (SDK) that Apple will release shortly, a lot of that will be alleviated when third party developers can create applications for it.
If you have a Mac, the setup should be fairly seamless. If you have a recent PC running iTunes, it should work too but I haven't tried it.
If you're not a Mac convert after using the iPhone, you probably will be after using it. Might be a great conversation starter and entry way into the gospel too because strangers will ask you about it.