i gotta say - i have the same phone, and i've never had a problem with the headphone jack, or the speaker... in fact, i've come kind of close to blowing out the speaker a few times......
you might want to check with whatever store/carrier you got the phone from. it might be defective.
also, extend the battery life by turning off your bluetooth, satellite, wi-fi, and all of that stuff...... i've gotten my battery to last for 2 days. you might want to consider turning off your 3-G too, but doing so will mess with your picture messaging.... it will save battery, but you will not be able to send or receive pic messages while it is off. your text messaging will still work tho. if you're low-low-low on battery, turn off your 3-G to save some until you can charge it.... but, if you're good, keep it on.