On my HTC Feeler (I-Mate SP3i, Qtek 8020, O2 XphoneII, Dopod 575, T-Mobile SDA, Orange c600(?) ) with WM 2003 SE.

First I installed Resco sound recorder, Vito Audio Notes, and PM Recorder.
None of these work on WM2003 (Resco tried to work for me, but failed)

So I went through the long and painful (for me) process of finding out how to upgrade to WM 5.0, and doing said upgrade.

Now running WM 5.0 I tried the same three programs: Resco, Vito, and PMR.
All seemed to work perfectly except that while they seemed to be recording calls correctly, the resulting sound files were just blank, with no sound of any kind from any source, not even static.
I tried every possible setting, but no dice.
If I just recorded something as a dictaphone they worked very nicely (Vito was my favourite: polished but not bloated.)

I gave up trying to get automatic recording whenever a call started, and tried to get just manual recording.
I tried the same three programs, starting them as a dictaphone after answering a call, the results were exactly the same as before: blank sound files.

I then tried RJV Sound recorder....same result, blank file.
NetDictate of course wouldn't run on WM5.

I was now desperate, I tried running my video camera during a call, but got an error msg saying there wasn't enough memory available.
I tried to see if the default voice notes program that comes with WM5 could record if I started it manually during a call, but it won't start during a call.

I know hardware restrictions in many devices means you can't properly record one side of a call, but I think this phone may be different. From my experience here I'd guess that the hardware makes it impossible to record anything during a call.

I've now given up, I can't record a call on my phone, unless someone can tell me about some software they've used on exactly the same phone and OS as mine, successfully.

If you are using Ronswen's excellent site Ronswen's custom WM5 ROMs and tute to upgrade from WM2003 to WM5 and are getting this error:

"Unknown error -2147467259 in read operation" in SPVservices

and later also this
"MTTYDownloadImageNot allow operation!" when doing the tty part,

it means your phone is application-locked (check it with checklock.exe)

To application-unlock your phone use a registry editor (I used RegEditSTG) to make these changes:
HKEY_LOCAL_MACHINE\Security\Policies\Policies0001001 = 1
HKEY_LOCAL_MACHINE\Security\Policies\Policies0001005 = 40

then run SDA_ApplicationUnlock.exe

Your phone will now be application-unlocked and you are ready to follow the instructions on the site.

Note: I upgraded an HTC Feeler/Sonata (I-Mate SP3i, Qtek 8020, O2 XphoneII, Dopod 575, T-Mobile SDA, Orange C600(?) ) from WM 2003 SE to WM 5.0