I have been using the Enable In-Call Recording tweak, but it has some issues, such as taking about 5 MB's per minute, and only storing it to the phones memory, which will cause problems on a long call. Then I noticed this:
http://forum.xda-developers.com/showthread.php?t=536472
Hopefully this isn't a re-post. This allows you to store the files anywhere, and adjust a lot of things, including 8 or 16 bit, sample rate for 8k to 192k, and 2 types of .wav files. I find the GSM 6.10 files take a fraction of the space as the other type (PCM). I tried all sorts of configuarations, and when with 192k, 16 bit (seems to be little difference in file size from 8 bit), GSM 6.10, "Ask to Save Call", "Record Incoming Calls", and "Record Outgoing Calls". The "Ask to Save Call" brings up a box that allows you to choose Yes or No, so you can leave it set to the Auto Recording In & Out, and still not save more than what you want.
However, the last call is always saved as Last Call.wav (or something like that), so if you say No by accident, you can get it back if you after made another call yet. That file gets re-written with every call.
I also have an issue with the old Enable In-Call Recording program. I CAN'T REMOVE IT. Tried the re-install trick, etc. It doesn't interfere with this new one, so no biggie, but I'd rather get it out of there. Anyone run accross this issue?
EDIT: CAB ATTACHED BELOW