It's certainly possible to develop on a Windows machine, in fact, my first application was exclusively developed on the old Dell Precision I had at the time :)
There are three routes;
- Install OSx86 (aka iATKOS / Kalyway) on a second partition/disk and dual boot.
- Run Mac OS X Server under VMWare (Mac OS X 10.7 (Lion) onwards, read the update below).
- Use Delphi XE4 and the macincloud service. This is a commercial toolset, but the component and lib support is growing.
The first route requires modifying (or using a pre-modified) image of Leopard that can be installed on a regular PC. This is not as hard as you would think, although your success/effort ratio will depend upon how closely the hardware in your PC matches that in Mac hardware - e.g. if you're running a Core 2 Duo on an Intel Motherboard, with an NVidia graphics card you are laughing. If you're running an AMD machine or something without SSE3 it gets a little more involved.
If you purchase (or already own) a version of Leopard then this is a gray area since the Leopard EULA states you may only run it on an "Apple Labeled" machine. As many point out if you stick an Apple sticker on your PC you're probably covered.
The second option is more costly. The EULA for the workstation version of Leopard prevents it from being run under emulation and as a result, there's no support in VMWare for this. Leopard server, however, CAN be run under emulation and can be used for desktop purposes. Leopard server and VMWare are expensive, however.
If you're interested in option 1) I would suggest starting at Insanelymac and reading the OSx86 sections.
I do think you should consider whether the time you will invest is going to be worth the money you will save though. It was for me because I enjoy tinkering with this type of stuff and I started during the early iPhone betas, months before their App Store became available.
Alternatively, you could pick up a low-spec Mac Mini from eBay. You don't need much horsepower to run the SDK and you can always sell it on later if you decide to stop development or buy a better Mac.
Update: You cannot create a Mac OS X Client virtual machine for OS X 10.6 and earlier. Apple does not allow these Client OSes to be virtualized. With Mac OS X 10.7 (Lion) onwards, Apple has changed its licensing agreement in regards to virtualization. Source: VMWare KnowledgeBase
The only way to communicate with other Bluetooth devices via the External Accessory framework in iPhone OS 3.0 is if they are in the Made for iPod accessory program. Even though they communicate through standard Bluetooth connections, accessories need special hardware in order to process the data stream coming from the iPhone / iPod touch. Unfortunately, this means that your idea of communicating with generic Bluetooth devices won't work on iPhone OS 3.0.
If the devices you want to talk to are Bonjour-discoverable via Wi-Fi, they don't need to be part of the Made for iPod program. However, that doesn't sound like your case.
Third-party developers in the near future may produce dongles that connect through the 30-pin dock port and give access to existing Bluetooth devices. If these developers opened up their communication protocol, that might enable your goal of communicating with these devices.
Best Answer
Not sure what the API will let you do but the Bluetooth Host Controller Interface (HCI) command underlying this is the 'Inquiry Command'
This will let you inquire about devices either for a fixed time and/or a fixed number of responses.
I'm a Bluetooth neophyte, not an expert but...
To get at least 1 response from a Bluetooth device that is in a low power mode takes 1.28 seconds, so inquiry time is in multiples of that period up to a maximum of 61.44 seconds (48 periods), so the time range is 1 (1.28 seconds) to 48 (61.44 seconds).
There might be several devices that could respond in a single 1.28 second period though.
You can also specify the number of responses you will accept (1..255) or 0 for unlimited e.g. until the time runs out.
You can also cancel an inquiry, if you found a particular device you were looking for.
Unscientific test from my desk using a CSR bluetooth chip with Bluetooth 2.1 +EDR firmware running inquiry on the chip with debug output via the chip UART. Ran each inquiry 10 times and took an average of the results:
I say 'unique', actually the results repeated a lot of the same addresses over and over, this may be implementation dependent though and the Apple API may only return unique addresses.
However, this is not representative of the 'real world' as most of the Bluetooth Devices around here (my office) are not in a low power mode. I guess, I could filter out PCs, laptops and test kit by Class of Device. That would get mobile phones, headsets that were discoverable etc...
Inquiry can also be combined with RSSI to get the the devices with the strongest signal but they may not necessarily be the closest.
For your scenario you might want to do an inquiry bases on time and number of devices e.g 4 * 1.28 seconds or 10 devices.
To summarise: The shortest time you can do an inquiry for is 1.28 seconds and that could get 10+/-? devices in the area IF they are awake and near by.
If you've got a saturated Bluetooth environment or (a microwave oven going in the same room) it could take longer to find all the devices within range.