My old iPhone 3GS' dock connector stopped working all of a sudden. After taking it to an authorized Apple service center here in Colombia, they said that it wasn't worth fixing, as it would cost practically the same as a new phone. I refused to believe that was the end of it and went on the web to see if I could find a solution.
I ended up on the iFixit website and, after reviewing the guides, decided to take the risk and try fixing it myself with the parts sold by iFixit.
The repair process went well, although it was a bit more difficult than anticipated for a newbie like me. I had to open the phone several times when I was testing the solution and, by the third or fourth time, I was already able to do it even faster than the video.
The dock connector worked perfectly, but I had to exchange the antenna that came with the part with my old one (which was working fine), and also had to exchange the microphone (my old one also worked fine).
Both parts weren't very good (very poor antenna performance and below average microphone performance). The antenna exchange was easy, as it doesn't require any soldering, but the mic was a bit trickier. In the end, it turned out fine and my 3GS is back!
If your old antenna is working, you definitely want to exchange it. You just have to peel it off the old module, do the same with the new part, and swap them.
Also, check the mic, the one that came with my part worked well at first but then started to quickly lose performance. The microphone swap does require soldering though, so you need to be careful and have a basic soldering iron on hand.