I would like to see SparkFun develop a Bluetooth to serial adaptor which could be used with an iPhone. The catch is you would need to become an official “Made For iPod / Works With iPhone” licensee.
What’s wrong with the existing bluetooth devices? Do you really need something specific to talk to the iPhone?
Correct. The iPhone can only connect to devices (via cable or Bluetooth) which are certified by Apple. I don’t know exactly how they limit access, you need to sign an NDA with Apple to find out.
I’m not certain what you mean. My 3G iPhone has no trouble connecting to my non-apple bluetooth headset. Is that what you’re talking about? I’m not aware of any bluetooth compatible device that it wouldn’t connect with (assuming both devices support compatible profiles).
It won’t connect to a Thinkpad.
About 6 months ago I wrote some software that ran on my ThinkPad to detect who was near me by learning the Bluetooth IDs of their cellphones. The iPhone was the only one that could not be discovered. The owner and I were both puzzled by this so he did some research and discovered that other developers had found the same problem. The iPhone will only identify itself to certain devices.
There’s probably a way around it, but neither of us was motivated enough to bother figuring it out 
Apparently you can ONLY connect to headsets. Everything else has to be an Apple authorized device. In the Apple forums there are a lot of people who would like to write iPhone apps (myself included) which would talk to other hardware devices. A serial interface to a MCU would be nice. I’m in the process of signing up for the Apple Mfi program myself so hopefully I’ll understand it better soon.
The new 3.0 SDK lets you add bluetooth peripherals to the iPhone using your own protocol.
You could in theory link to any Bluetooth PC, but would probably need custom PC software too.
Its mainly designed for linking to iP(od)hone accesories like remote controls, nike+,pedometers etc.