Assuming I have an idea for an iPhone Gadget like this: Griffin-Simplifi-iPhone-Reader-Aluminum I am a creative person or a designer. If I want to realize this product to whom do I have to go, to find out how to create the electrical circuits, where to produce e.g.?
I seek to understand this whole product life cycle and would also appreciate some resources for further reading.
I am not sure exactly what you are asking, but to get the pin-out specifications and sell interfaces to ipods/iphones/ipads you need to work with Apple. I went through this process and it is a hassle. They are very draconian about the terms and partnerships and they take $5.00 for every device that is sold that interfaces with their product (even a cable).
That is just the part to legally work/interface with an iDevice. I suspect your question was where to get electrical engineers to build your product. I don't have any advice for you on that.
As Tim mentioned, you are going to have to sign a contract with Apple and pay them a fee.
I take it you are the idea man and want to locate someone who can turn your idea into an actual product. You need to realize, up front, that this is a fairly expensive and multi-step process. You don't just walk into an engineering firm, tell them you idea, and come back a few weeks later to pick up thousands of your products to sell.
First you are going to need working capital. To produce a single working engineering prototype you will need from $50,000 - $100,000. (Price depends on the firm and how complicated your idea is.) The engineering firms are not going to work for free or on spec.
Second, you need to locate a firm that has a successful track record developing the type of gaget you want to build. It would be helpful if this firm has a working relationship with several Chinese manufacturers- where your device will ultimately be built. You locate this type of firm by recomendation- you need to find firms that have done this before.
Third, you need to test your product prototype. You have to work out the bugs, develop product styling, do consumer testing, and get the device ready for manufacture.
Fourth, you set up product manufacturing, typically in Chian. You will need the help of someone who has done this before. The Chinese will redesign your entire gadget and you have to make sure their redesign does not change or wreck the product.
Finally, you need to get a UPC number for your product, set up distribution, and advertising.
Note some people skip the local design and testing and jump straight from product idea to design and manufacture in China. I do not recommend this approach. It is exceedingly difficult to get a product initially designed in China (they do it for free). In addition, you usually find your product being duplicated and sold by other firms when you take this approach.