Okay, it's not really hacking, but Nokia Beta Labs has released a nifty little app called Mobile Web Server. It runs on Symbian OS an it lets you wiggle into your mobile from the web. Actually, it creates a webite at username.mymobilesite.net
Once in, you can read your messages, view your pictures and check your call logs. You can even take command of your mobile's camera and take a snapshot remotely. I can see how this may develop into an insanely useful piece of software. At the moment the connection is pretty slow and it slurps up battery power, but give it time.