This URL can only be accessed via Cydia.
Just add http://hacx.org/repo/ to your Cydia sources list (Click Manage->Sources->Edit->Add).
Inside this repository you will find the well known tweaks - "Super Recorder" & "Call Recorder" - the ultimate iPhone call/voip recorders and Voice Changer.
Alternatly, if you have Cydia installed, you can click this link to add the repository:
Automatically Add Repository