Apple wasn't very specific on the "extended parental controls" it was pushing into the 3.0 firmware release. However, you can use a $12 Cydia-based application called iBlacklist to create white and black lists of who's allowed to call / forbidden from calling an iPhone. You can then schedule the activation of these lists according to certain time intervals--perfect for keeping the kid off the iPhone during school hours.
Finding a free application to mimic the 3.0 firmware's new audio recording feature is tough. The Apple Store-based Evernote application allows you to create audio memos, which you can upload and save to the online service. And the free YouNote application lets you draw, text, or record notes straight to your iPhone. Cydia's counter is Cycorder, although this app is more geared for taking videos with your iPhone than direct audio notes. Unless you want to pay anywhere between $1 and $5 for a solid audio recorder Apple Store application, YouNote might be your best bet.
Turn-based GPS navigation
Finally, the iPhone's included Maps application takes a page from nearly every single GPS device imaginable by offering turn-based navigation. However, a free Cydia application called xGPS not only mimics this functionality, but it offers location bookmark functionality, English voice instructions, and incorporated Google terrain maps for outdoor adventurers. In short, xGPS turns your iPhone into a GPS.