I have 2 I300s. I want to swap face plates, one is in better shape than the other. Can this be done? Easily? Will I have any thouble with reassembly?

First of all, you need the tiny Torx bit that nearly every cellphone uses. Yeah, that one. Good luck finding it. As for the screws, there is one in the stylus seat, one directly to the left (covered with a little plug), and two more behind the battery.
When prying it open, you want to use a cheap, dull, and flimsy-as-can-be knife. I found an el cheapo serrated steak knife that works really well.
What you are doing is prying the faceplate a little wider so that the side locking tabs aren't as much of an issue. (They'll still give a little trouble.)
slide the blade up from the bottom. Twitch it inward. You'll feel and hear a pop.
Now, do this on the other side.
After you have done these steps, carefully pry the back plate off, starting at the bottom. There is an ext. antenna plug and the seats for the two upper screws creating a potential hazard for the motherboard and the bulkier circuitry upstairs. You have the antenna plug, LCD alert screen, IR transceiver, earpiece jack, and the board itself to worry about. Pry the sides of the front half outward (gently!), and finish pulling the front off at the top.

Thanks for the detailed response.

What did you do to your phone to have such a knowledge on the construction, inside and out?

Yes it is fairly easy, just be sure not t scratch then housing when you pry the snaps. Also make sure the microphone and speakers are seated properly and the metals contacts are alligned when you redo everything. btw you will need a t5 or t6 screw driver to open it, forgot which one.

My first shot at a decent i300 was a dud. I didn't find this out until I got the rest of the accessories upon my return to TX from Memphis. I promptly ran the smoke test. No dice. Screen: check. Touchpad: DOA.
Fortunately, the accessories I bought from another EBayer included a phone with screen problems: So, I tried cannibalizing the two units, in the same way I got both my 6035 and my pdQ working again.
The i300 was weirdly set up inside. Sure--the basic principles were there: the mobo and the video card were separate. However, the circuitboards themselves were not engineered, really, to fit the case as much. That was one obstacle: one bad flip of the wrist, one miscalc with the knife, and voila, one cracked piece of silicon would've been in my possession.
The other obstacle was the case itself: the likelihood of case breakage was indeed high--more so than with either of the Kyo/Qualcomms. At one point, I was wondering how in the name of all planar existence they assembled the machine without culling enough breakage to pull profits into the toilet of excessive recycle costs.
To make a long story short, I forgot that it's easier to bum a solder kit from a computer geek and replace the whole sensor assembly than it is to take a razor blade under the sensor sheet and stick it on the other card...or trawl Ebay again and find yet another unit. Too little, too late.
Oh well. Forsan et haec olim meminisse juvabit.