The home button on the phone was not working.
the repair went a bit bananas at the begining. I replace the part and one of the internal cables was not doing good contact so i could not use the slide functionality on the screen. I reopen the iphone and connect carefully the cables again. Then it works.
Iphone 3g works like new.
I can see that the screen is not the same type as the original one but it work so i will survive.
it si a challenge but it was fun.