A variety of Bluetooth keyboards are now available for paired use with the iPhone, iPod Touch, and iPad. Many of these are mini-keyboards with only a subset of the keys of the Apple Wireless Keyboard, or requiring the press of modifier keys like an "Fn" key to activate alternate functions. You can have VoiceOver announce these key functions by entering keyboard help mode or by visiting the practice gestures area of the Setting menu as an alternative to pressing the Control-Option-K keys on your keyboard. Then subsequent key combination presses will be announced by VoiceOver, until you exit help mode by either pressing the "Escape" key or the "Home" button. Some keyboards have additional keys that work like the "Home" button or that take you to the "Search" page (like similar keys on the iPad Keyboard Dock).
The alternate way to enter keyboard help mode for your paired Bluetoooth keyboard when you do not have a Control or Option key (or do not know where they are) is to navigate to the VoiceOver practice gestures area on your device: Settings > General > Accessibility > VoiceOver > VoiceOver Practice and flick right past the "Done" button to the area of the screen for practicing gestures. If you have paired a Bluetooth keyboard, it will now be in keyboard help mode, too. You can enter VoiceOver help mode through the practice gestures area, and you can exit this mode either by pressing "Escape" or "Home" on your paired keyboard, or by double tapping the "Done" button in the top right corner of the practice gestures area screen. Incidentally, this also works the other way around: entering VoiceOver help mode from the keyboard of your paired Bluetooth device (by pressing Control-Option-K) also makes all your gestures made on the screen of your iDevice behave as though you were in the keyboard practice area of the Settings menu even if you are not in this area. Your gestures are announced, but not acted on, until you exit this mode. This can be a useful way of checking new Bluetooth keyboard key functions.
Also note that on keyboards with "Home" keys, double clicking this key may take you to the App Switcher, and triple clicking may toggle VoiceOver on or off. In addition, even on keyboards without Control and Option keys, the arrow keys can be used to turn Quick Nav on (by pressing right and left arrow keys simultaneously) and then used to navigate the screen (right arrow press for flick to next control, left arrow press for flick to previous control; up and down arrows pressed simultaneously to activate buttons or links (double tap), and similar combinations to move to previous rotor (up arrow + left arrow) and next rotor setting (up arrow +right arrow). Up and Down arrow presses will move through rotor menu options.
Mac users also have the option of pairing these keyboards to their computers, and using their default keyboard to initiate/exit keyboard help mode (e.g., press Control+Option+K on your computer keyboard, then check the key functions of your Bluetooth keyboard in VoiceOver's help mode by pressing key combinations on your Bluetooth keyboard). This is similar to the method of using the practice gesttures area on the iPhone, iPod Touch, or iPad to initiate keyboard help mode when you don't know how to do it from your new Bluetooth keyboard, in that you use your computer's keyboard and VoiceOver to enter keyboard help mode. The process is slightly less direct than testing the new keyboard on your iDevice, since some of the announcements for OS X will be slightly different than for the iOS system used by mobile devices.