In general, this is a great concept. I like the calculator much better than the standard S60 version. There are, however, a number of things that make it less than it could be. Some of these items have been mentioned before.
1. The application takes a long time to load.
2. The background on the E71 is all white instead of just the entry area. It is also off center in the screen. Not a huge deal, but it could be better.
3. All basic math functions should be accomplished from the keyboard rather than having to bounce between the keyboard and navigation key. + should be for addition, * should be for multiplication, not navigating through functions, - should be for subtraction, / should be for division. Pretty simple change I would think. Also, the Delete key should Delete and the Enter Key should solve the equation. It would also be nice to recognize the additional symbols in the E71 keyboard such as %
4. It would be nice to have a Memory Clear button in addition to Memory Store and Memory Recall. This button is pretty standard on most calculators.
5. Last thing is it would be nice to have an "About" menu under Options so the user knows what version they are using.
If you can correct the above items, it would be a stellar app worth 6 stars.