At Google I/O 2011: Chrome Dev Tools Reloaded, Paul Irish and Pavel Feldman introduced new remote debugging feature — which was in passing included into webkit.
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Just because a feature is implemented in one port of WebKit (in this case, Apple and Chromium), does not mean it is always available elsewhere. I wrote this in details in my blog post about different WebKit ports implementation.
So far, the only mobile WebKit port which has the remote debugging feature is RIM Playbook browser.
For iOS, it is very difficult to know because Apple does not give any information about its future product ever. At least we know that iOS 5 will not have it since the beta versions do not show anything related.
For Android, definitely it is coming in a future release, since Android folks are adopting Chromium as the new basis for its WebKit.
Take a look at this bash script to start the remote inspector with iOS simulator: https://gist.github.com/2241976