Since taking a job with AT&T (specifically focusing on iPhone support) the most repeated question I have received other than, "Can I get on a reserve list?" is; "Can I print from the iPhone?"
I have to be honest and say ... I don't know.
The iPhone does have Bluetooth. I personally own two Bluetooth printers. The first is made by Kodak; a nice Bluetooth photo printer called the EasyShare 500. The second is made by HP; a wireless printer called the 450BT (the current model is the 460wBT). (see pictures below)
I say there is a good possibility that the iPhone will be able to print via Bluetooth. If Apple advertises this as "this isn't the watered down version of the internet" - I say the internet is printable. If they advertise "a phone like no other" - I say the average smartphone is VERY difficult to learn how to print from - if you can print from it at all.
This is one thing I loved about the Newton. If you bought an Apple Stylewriter inkjet printer - boom - you were printing with little to no effort.
If I understand Bluetooth correctly - it is a standard in and of itself - for any type of protocol that it is assigned. Meaning - if a "certain something" has the ability to be paired and/or discovered via bluetooth - then it should work.
I know that with both the Kodak and HP bluetooth printers that I have - I did not have to load any drivers and I do not think the drivers were in my basic OS install for these printers.
I would love to hear reader thoughts on this.
[ANSWER] NO ... at least not yet.
[UPDATE] One can now print from the iPhone via HP e series wireless printers. These are the ONLY printers officially supported at this time and can be found at most office and electronics stores online and at retail for $75 and up to $399.99.
ALL HACKS that enable this feature on "other printers" require a very complicated setup and require a nearby computer to be turned on and used as a server.
[UPDATE] The latest iPhone OS 5 allows printing.