whell, it's possible. oh.. it's not like to discover hot water.. but never easy as drinking it.
-be skilled in manually, and dare.. with courage
-read a lot of guides to assemble/unassemble i4.. BUT
most of them are incomplete because explains (very clear) what to do about repair/replace .. and the difficult is to learn the assembly of little parts.. which are hidden or intended to be 'always mounted' and never unassembled (as the balance lever to extract sim, the complete exploding of mute/unmute lockbutton, the correct position of the small grids between ear/mic and middleframe, how to place stickers/wificable, and not less important the exact bill of material of screws.. they are huge.. and starts from 1.2mm to 6mm! what you must put and where??)
-buy the parts with calm.. you must be as the man who's waiting on the dark side of the river..waiting that the dead passes by.. Ebay bids are damned.. and you want it now.. no. you want it before now. you want to have iphone4.. right NOW. and you pay a lot if you move faster. be quite. (repeat 10 times)
-remember: paying 30 things to 30 sellers.. and you spend a lot in shipping. my 1st experience is that: due to have the iphone before summer.. I want to close bids everywhere.. to have all items before summer. wrong. I spent 80€ in shipping.
see the attached xls.. same color.. same seller. I bought items in different times from different seller.. that's because I never knew the complete BOM until I finished to mount it! so.. now I know.. next i4.. I'll be more saviour.
-never buy locked logic boards.. some BaseBands are impossible to unlock.. and sincerely.. it's very boring to spend time .. a lot of time.. to unlock a thing that's unlockable.
I'm here to advice you.. ask me.. not PM
in attached the BOM.. the name of my sellers.. they're not the best.. I suppose HK sellers do best price..
I wrote all .. because you can learn what parts are needed
I think I've forgiven 2 or 3 things.. but because I don't have data! they are:
-the little metal rectangle that covers the flat near the connector of the battery
I think I could spend less money.. suppose between 300 and 400
but it depends on how you buy logic board... because the average of the cost of the Group Display/Digitizer/homebutton/dockconnector/backcover is near 95..110€ (black or white)..
sorry for poor english