Ok, I had mcleaner working just fine and dandy when I was jailbroken on a 2g iphone on 3.1.3. Mcleaner does NOT work on 5.1.1 though. I installed it, made a phone call, it froze when I pressed "end call" and I had to restart the iphone. I uninstalled mcleaner and the phone app worked perfectly again. The phone was working just fine before I installed mcleaner so I KNOW mcleaner is the culprit.