German's official rules for grammar and orthography are rather clear in this case. The following words are names (of brands) and therefore nouns. All nouns are written in German with a first uppercase letter, while the rest is written in lowercase letters only. By following this rules we get:
But ...
... languages are developing, and the official rules can be seen from two points of view:
Rules define what is right and what is wrong.
This is a good point of view for teaching and learning a language. You are not a German native speaker and want to write a correct German sentence with a meaning that you have in mind? Then you will be happy that there are books that contain the rules that will help you to create correct sentences.
But when you speak or write in your own first language, will you then always produce absolutely correct sentences? And what about the words you use? Do they meet all hardcoded rules of your language? I don't think so. Because there is an other way to interpret rules:
Rules reflect the in-fact usage of a language.
Which was first? The rules or the language? When you was a baby and learned to speak, did you start with learning the rules? Certainly not. And when you speak to a friend in a pub or on phone: Do you think about which rules you have to use to build a sentence when you tell your friends about your last holidays? No, you don't.
But implicitly you always use rules, and the “official” rules just try to be a clear and compact catalogue of all those implicit rules. But a language is a living thing. The implicit rules that we use every day are much much more complex then the hardcoded rules in your grammar books. And some of rules can change quickly.
When ever one of those implicit rules changes, and conflicts with the “official” rules, always the same things will happen:
- There will be some people that give a sh.. on conservative rules and write as they want to write.
- There also will be some people who believe that this is the end of culture and moral in our land. We have rules! Follow the rules!
- After some time more and more people don't follow the old conservative rules that are written in grammar books. They follow the implicit rules that are in contrast to the written rules.
- Again after some time, the authors of grammar books see, that out there in the wild is a vivid rule, that is not in their book. Now it's time to write this new rule into the book, or to change one of the existing rules.
In case of eBay and others this means, that nowadays we have the conservative rule (all nouns have exactly one uppercase letter, which is the first), and in addition we have a small group of nouns, that are an exception to this rule. They do not start with a capital letter, but their second letter is written as a majuscule. And the first letter (which always is a vowel) is a separate syllable, and the word os pronounced like an English word.
So in real live we use
iPod
iPad
iPhone
eBay
But until now not all of this exceptions found their way into the official books of orthography and grammar.
btw:
None of the words we are talking about here follow the rules of any language on this planet. There is no language who's rules allow to write the first letter lower case, the second upper case and the rest in lower case again. This is wrong (according to conservative rules) also in English.
Just some words about “I-Pod”:
I think this the attempt to create a word, that is similar to iPod, but follows the conservative German rules. But nobody used this variation. If it really is in Books like Duden (which I didn't check), then I'm sure it will not stay there for very long. The factual usage is “iPod”.
