Faulty headphone jack? (and some newb questions)

Hey folks,
I bought a 2nd hand iphone the other day, and have some questions about it and iphones in general.

Firstly, the headphone jack seems to be faulty. When I stick the headphones in, the right sound channel gives out no sound. When I lift the headphones up in the jack by about 1mm, there is sound then. That's fine, but if I have the iphone in my pocket when walking about it'll be disturbing the sound.

Any advice regarding this?

Also, I bought the iphone jailbroken, but the battery life was god-awful...remaining power dropped by 1% literally every minute or so when I was using it. I read somewhere that jailbreaking can make the battery appear to be terrible, so I restored the iphone to factory settings and the battery seems grand now. But I'd like to jailbreak the phone eventually. If I do so, will the same thing happen again?

I'm on O2 PAYG, and don't have anything set up regarding data packages...is there a recommened PAYG data deal or something that I should get in order to use the iphone for internet usage when outside a wifi spot?

Finally, is there any way to isolate the volume control of just the ringer and messages. ie if I'm playing a game and the sound is too loud I'll turn down the volume, but then I have to turn it back up again when I'm done so I can hear a phone call come in.

Thanks v.much for any help!