Ask HN: Is it possible to have hidden call recording app on Nokia S40?

I have a phone who's owner suspects wiretapping and asked me to check. There are apps that claim this possibility but the platform doesn't look advanced enough for this. Also this app should be hidden as there's nothing suspicious in app list now (or maybe it's some kind of self-destructible). I highly doubt it's possible at all as platform should support hidden apps and heavy background tasks at the same time but I'm not mobile developer so this is just a guess. So is this theoretically possible and, if so, is there a way I can check to be sure phone is (not) clean? Thanks.