I've found a bug that allows you to produce a result above the possible range, however, due to rounding and the maximum 10 digit number, the result it shows on screen is out by a factor of 10.
9,999,999,999 + 1 = ERROR
9,999,999,999 + 0.5 = 1,000,000,000
This should procude an error, seeing as the number it should produce with rounding should be 10,000,000,000.
This bug will only pop up when the *actual* result of a calculation falls within the following range:
Lower limit: [10,000,000,000.40000004]
Upper limit: [10,000,000,000.50003910]
I have tried to achieve similar results on an older 3310 phone, but the error checking seems fine on that one, also it could only handle a 9 digit number.
Just out of interest, have a go on your nokia or other phone and post the results here.