GTune is a free guitar tuner for your S60 2nd edition mobile.
It has very accurate algorithm (less than 0.5 Hz possible mistake), friendly interface (graphical guitar neck), noise level setting and tone generator.
Guitar used for testing: Admira Rosario 
Downloads and support at: symbian.boo.pl
This is a very useful tool. However I have seen it panic quite often (not during tuning luckily). Tuning is not so easy, because the app does not recognise the tone (base frequency) very steadily. So the point flips around quite often. I used a mid-quality Western Guitar with light strings.
Additionally a cent display and a better "middle" marker in the black "tuner field" would help.
Also the tones play only very short. They should loop.
Besides this, it is very fine!
Best regards, Marcel
Those panics were caused by unexpectedly high frequency - e. g. when you whistled. I have issued a new version which solves that problem.
As to the accuracy: please read the help and experiment with noise settings. By "noise" I also mean harmonic sounds of the guitar itself - the cause of algorithm hesitation
symbian.boo.pl
hi
GTune is really a revolutionary product. I went amazed once i used it on my Symbian based Nokia phone. But presently many more cool applications have come up for S60 based phones. Recently i found an elaborate list of Top 20 S60 based applications on Realgeek..Have a look at them too..