You can use any call recorder. heck you may use pys60's sound module and code your own (I have

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But remember to disable the beep only using a patch from rompatcher or modding the firmware itself. this will disable the hardcoded beeps and you may then proceed to record with any app in the best quality possible.
You can use Ultimate Voice recorder too but remember to disable the no beep function of these apps because all they do is skip recording after every few seconds interval like 5 seconds, so the recorded file is lossy and of lesser duration than the call.