Distributing iPhone Apps To Private Clients

Since I am new to iOS development I have a few Questions. Firstly I did read some of the other related questions I just want to clarify a few things.

As I understand it:

1. I can make an app for a client and then the client can purchase the app for me and register a Enterprise account and then be able to distribute the app in house. But they need to have 500+ employees to be able to subscribe for Enterprise.

2. I can make an app and distribute it to end users in the normal manner. Nothing funky about this.

Now my questions are, what way should one go about when you want to create an in house app for a client with less than 500 employees, which means they can't register for a enterprise account? And is i开发者_开发百科t posible to list an app for free on app store but you can only use it if you have a license code that you need to enter to unlock the app, so basically when Jon Doe downloads the app he can't use it, but if the client downloads the app they enter the code and the app then gets unlocked?

Edit: Not Applicable Anymore, See Edit 2: Ok did some more research, another problem I will be facing in the new future is that South African companies can't get a DUNS number which is required for the enterprise license, so basically that route is blocked for me, because of that problem. So what other way is there to go about this?

Edit 2: After some further research I found that the DUNS number can be obtained outside the US and that South Africa is listed as a country in which a DUNS number can be obtained. Can anyone out side the US and mostly outside Europe confirm that DUNS numbers are available in their countries, and actually know of companies in there country that has one. And I know I am going of topic but how can I check if a company has a DUNS number.

Thanks

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First, most probably the 500+ employee restriction is not applied any more for enterprise distribution. But, the company which want to apply for enterprise development account need a D.U.N.S registration number.

The other way to distribute the app is to use ad-hoc distribution. You can have at most 100 mobile phones in your company where you install ad-hoc version of the app.

You can make an app with an access code and mark it free in the app store. The app can be used only some people who have the access code. But when Apple people will review it, you need to give an access code to them too, to review and see inside the app. This is absolutely legal. And it works.