I was on a call a while ago and wanted to verify that someone didn't call me a few days ago. I couldn't figure out how to open the call log while I was in a call.

When I'm NOT in a call I open the phone app and there it (or a subset?) is.

Thanks

Not sure whether there's any built-in way to do it, but you might want to take a look at the application "Extended Call Log" (should be in the maemo.org repository, I think). Since it's a stand-alone application, it should be possible to open it while on a call.