Jail-breaking and unlocking my iPhone 3G, HELP ME!

Alright, I know this is probably just reinforcing the stereotype, but as a 20 year old female with a slightly-higher-than-basic knowledge of computers, I am coming to Reddit to beg for guidance.

Long story short, I was given an iPhone 3GS to replace a Blackberry Torch that, in my clumsiness, I dropped and was rewarded with a cracked screen. Thankfully, the iPhone was free and I used it to my heart's content. For reasons we won't get into, I unfortunately had to return the phone. (Let me just add here that the person who gave it to me is an absolute douche for the whole situation.) I now have my SIM card back into my shattered Blackberry Torch, however, the phone is slowly dying on me. The touch screen barely works, the scroll pad is destroyed, the phone will shut off in the middle of calls and is just being a general pain. My boyfriend was able to get a used iPhone 3G in my hands which is updated with the latest 4.2.1 FW and 5.15 BB. The only thing is that the service provider that the previous owner used was not the same as mine, so, I've got to unlock the phone. I could make things easy on myself but VERY tough on my wallet and call my service provider and ask them to unlock it, however their charge is $50 and I am NOT willing to go to any unlockers and pay them $15-$40 to do something I feel I could do with on my own. This may sound cheap, but I am scrounging for every penny I can, it just doesn't seem worth it.

So now, here is my problem... From my research online, it seems that I need to update my BB to 6.14 in order to unlock my phone... Though I have to admit I am lost on how to do this. The other steps I seem to have a good idea of what I need to do, but since the first step is totally lost on me, I can't exactly get started. I am very well aware of the consequences of jail-breaking & unlocking. I do not hold any warranty agreement with Apple, have no interest in further updating the phone once I am able to use it, and understand that by not doing this whole process properly I can literally turn this phone into a paperweight. I suppose this is where you come in, Reddit... Help me find the safest route to unlocking and jail-breaking my phone? Pretty please?

TL;DR: iPhone 3G running on 4.2.1 FW and 5.15 BB needs updated to 6.14 BB and to be jail-broken and unlocked. Best method pwease?

Thanks in advance.