I don't think anyone is arguing that the 30% is the actual cost to Apple, there's no question there's tons of profit baked in there. But Apple is providing services for that 30% such as download hosting, billing, collections, subscription management, etc.

The apps that use other billing providers are not selling digital goods.

Of course you can, I have such an app in the store. A telephony app where you can access all features without the app. (You just dial one of our local numbers and that will be mapped to a foreign number)

So this argument doesnt make sense.

False. You don't charge people through the app.

We do within a webview. Whats you problem that you believe you've got to explain to me how our app works?

Seems like you don't have a clue what is actually possible.

Go read the TOS for Apple's in app billing.

Sure but you aren't charging for digital goods. You are charging for infrastructure access, which is explicitly allowed.

Seems like you are trying to muddy the issue by pretending your case is representative of anything we are taking about here.

What we are doing is all digital. You buy credits on a website which you can use to call someone on a landline/mobile phone number.

Our only infrastructure are VoIP servers.

The infrastructure is not different than Spotify's. It's all just servers.

Well that's clearly not correct.

The service you provide to the customer is use of your VoIP infrastructure. That's what they pay for.

In the case of Spotify, the service is not access to infrastructure. It is access to digital goods in the form of licensed music files.