I have a hacked 2g and apparently my friend who installed everything didn't realize the phone dialer part was a trial. Now, all features of the phone work, but when I press the 'phone' button, nothing comes up. I can receieve incoming calls and can make a call through my contacts, but I cannot use the dialer or see missed calls / call log. I don't know what to download or what to reinstall.

u mean the stock phone app was a TRIAL ...
i dont think that is the case ...
a restore should fix the problem....here is a good guide :
iClarified - iPhone - How to Unlock/Jailbreak Your 2.x.x 2G iPhone Using QuickPwn (Windows)