Q: If I were to connect a Micro USB adapter to my iPhone 4, and then insert a Bluetooth 4.0 adapter into the Micro USB adapter, do you think it would be able to work with Bluetooth 4.0 devices?
A: Unfortunately, this wouldn’t work as iOS doesn’t include the necessary drivers to access third-party Bluetooth adapters via the Dock Connector port using the normal Bluetooth protocols.
An individual third-party app could theoretically do this by incorporating its own Bluetooth stack, but you’d be limited to using Bluetooth 4.0 within that specific app only; since iOS apps cannot run in the background to act as system extensions, it’s not possible to create an app that would act as a driver or “bridge” to an external accessory.
The only Dock Connector or Lightning Connector accessories that iOS provides native support for are keyboards, MIDI adapters, game controllers, audio input and output devices, GPS devices, and Apple’s own Camera Connection kit for transferring photos. Many individual apps provide support for connecting their own hardware accessories, such as health monitors, but these are usually a software/hardware pairing solution from the same company.