I put iOS 4.1 yesterday, it seems that the APN settings menu was removed. I had to go through
this to configure it again.
I'm still have issues with the network though, but I guess there is no fix for it. I'm closing this topic :)
Thanks!
PS: In case you're wondering why I didn't update to 4.2.1, I wouldn't want to have a tethered jailbreak, it's just not worth it for me.