Here is my story and advice regarding fixing your own smartphone.
Last week, I stupidly left my phone on the roof of my car and drove off, resulting in the phone flying to the pavement at about 30 MPH. Happily I recognized the situation immediately, and found the phone... with a shattered LCD.
My phone still worked, but the front glass was shattered, resulting in (at least) a painfully embarrassing handset.
At first, I thought I'd take it to a local shop to fix it. They charge about $90, which I thought was a pretty good deal. But then I saw that I could by the LCD part and fix it myself for a mere $30! That was a $60 savings! So why not?
So I went to my favorite on-line shop and bought a kit which included the LCD touchscreen and a specialty toolkit for $30. A few days later it arrived in the mail, exactly as I expected.
Then I went to iFixIt.com and checked out the instructions. There were about 27 steps to get at the screen... but none of the steps seemed to hard. So I cleared off my desk and started to go at it.
I have the patience of a saint, so I methodically followed all 27 steps to get to the LCD. I swapped in the new panel, and then followed those 27 steps backwards until my iPhone looked whole again. In all, it took me about 2.5 hours, with no lost screws or parts, and no "oh no" moments.
At the end, it all worked! I had a new screen, and I am totally happy with my repaired iPhone.
But was it worth it?
I saved $60 by repairing my phone myself. Was it worth it? Would I do it again?
I conclude that it would have been better to spend $60 more in order to get the job done professionally.
First, most people do not have the patience or the mechanical fortitude to deal with dozens of screws, connectors, and contacts, each which must be cared for perfectly.
Secondly, even for me, there is a lot of comfort in someone else taking responsibility - if I screwed up, I'd have 10 ounces of electronic waste. If they screw up, they are responsible for getting it right.
So in conclusion: unless you can afford your own failings, I suggest taking it to a quality shop and forking over an additional $60. That $60 buys you several hours and a valuable warranty.
Other facts of note
I did notice that the vast majority of the screws are there to hold down electrical connectors. It is amazing how much additional cost and effort goes into each connector on a phone. The connectors have to be screwed down, because no one wants them coming loose during a simple drop.
I can see the beauty of having as few connectors as possible. A higher level of integration results in fewer connectors, which results in higher reliability and lower cost. That means that phones are going to become much more highly integrated than they already are today.