I need to do this for the Soundcloud API and I have no idea what this is about or how to do it. There is a form on the Soundcloud API Developer website where you save your callback URL, but I'm not sure what sort of information I should input there.
Any help?
i believe this callback url is for oauth authentication, correct? i needed to do the same thing for twitter and ended up setting up a custom url scheme for my app (ie appname://oauth) and using this as the callback url.
in case you want to try this, see this article on how to launch your app via a custom url scheme. specifically for twitter, you can see jaanus's post on some implementation details and the github project.
while i haven't integrated with soundcloud, i did find that they have an objective-c api that you may want to check out if you aren't already here.
update
so what i mentioned is true - that you can use a custom url scheme and such to handle the authentication, but it's not exactly required. i found this article which outlines two methods for authentication - the first is for ios4 only and requires very little code. the second should work on 3.x and uses the custom url method i mentioned above (and outlines how to use it to authenticate).
so to answer your question once and for all, i suggest you:
look at this readme for the objective-c soundcloud api.
read this setup guide.
then read this usage guide.
check out this test iphone application.
hope this helps!