"Can anyone tell me if it is possible to work with fractions on the Iphone application or any other app for the Iphone and how?"
Perhaps the obvious answer to the question exposes that the question is asking something more than the obvious, so I'll just check it out first, ok?
The obvious answer is "The iPhone contains a Calculator (simple and scientific) and 'yes' it is therefore possible to work with fractions with the iPhone just as it is with any calculator"
You refer to the "Iphone application or any other app" which suggests a different expectation from those offered simply by a calculator?
The 'how' in the last part of your question could result in a text-book in its own right at one level or in a simple 'use the calculator like a calculator' at another level.
In trying to be sure
and to be helpful I'm probably confusing and sounding unhelpful, but the answer to your question is either so blindingly obvious or so deep that it's necessary to cover the extremes to be
really sure!