I have replaced the display assembly once and it was time intensive and grudgingly slow because you don't want to tear any of the flat wires but I was thorough and diligent and it paid off.
Something they do not tell you in this guide is to create a diagram of the iphone and draw where each screw goes as you remove it because there are more screws than I am sure of I can provide you a precise number but some of the screws are different sizes so you have the potential of damaging your phone or it not working correctly upon reassembly. I actually traced the phone, drew out each part and screw then taped the screw to the piece of paper.
Note: Be careful working on a surface that is not flat because if you are working with the screws there is a possibility it could fling off the paper and it does not take much for this to happen so be careful people and good luck!
When I took out the old headphone jack assembly the secondary mic was still attached to the housing because there was so much adhesive on it. be very careful when taking the old unit off so as not to remove the adhesive part unless you have more of it.