I'm experiencing similar, irregular issues on my 1st Gen iPhone (3.0, jailbroken w/ Pawnage tool). Sometimes my ringer won't ring, and when I try to answer, I can't hear the other person. If I miss a call, when I wake-up the phone (to the lockscreen) it'll still show an incoming call from someone even though the call attempt was made long before I tired unlocking the phone... Very strange. Just waiting on my new 3G S so I can look forward to JB'ing that, hopefully w/out these issues