Hello problem solved!
Look, it isn't exactly with WIFI. But within the Itunes system.So:
1/Connect the Iphone with the Itunes by the USB cable,
2/Go to Summary...scroll down the third box:OPTIONS,
3/And reorganize (for eg I've put tick for Automatically sync when this Iphone is connected + Sync only synced songs + Covert higher bit rate...) it's important to NOT tick the "Sync this Iphone with WIFI" (that's basically what's crapping the thing)
4/Go to MUSIC from the upper options near the Summery one,
5/Tick or do the playlists and whetver,
6/Sync,
7/Wait (probably because you have much music or the fact that they are being converted from mp3 into AAC),
8/Check your Iphone and VOILA! XD
Seriously, I've been hating myself carying two Iphones like a CEO for the past 1.5 weeks lol
When I finally sat down to fix this, turned out it was in the settings.
So Apple still rocks =D