I have added a ta.lproj (Tamil localized project) for my app and created localized Tamil strings.
When I wanted to verify that the localized text are correct, I found out there is no way I can do so because iPhone language settings (under General > Languages) does not support Tamil.
But I have seen apps in App Store that has Tamil as a supported language.
Is it possible to localize an app for Tamil?
No. Tamil locale language is not supported.
Did you mention here about mtamil-i? If so it was created by using images.
You should create your own custom keyboard then.