I use an Android app called SSH Tunnel I'm sure there is an equivalent for the iPhone ssh tunnelling isn't exactly rocket science.
To use your Pi as a ssh proxy just have Raspbian running and make sure your home router has a port forwarding rule created otherwise the Pi cannot receive incoming connections.
For security purposes you should change the pi default password and use an uncommon port number for ssh like 94, 89 (22, 1080, or 8080 is likely to to flag suspicions activity).
Change / add port number: sudo nano /etc/ssh/sshd_config and add line: port 89 (save and restart the Pi).
Next change pi default password with: passwd
Next make port forward rule on your router with TCP 89 pointing to your Pi's IP local address.
Next make a note of your external IP address and bung this into the iPhone app with username: pi and password: (whatever it is).
Now try and access websites with the iPhone your LNK light on the Pi should blink rapidly which would indicate traffic is being re-routed.
The nice this about SSH proxy it's encrypted so no chance of stealing data or know what sites you're visiting except for knowing the IP address of your Pi.
If at school you find that it doesn't work then your school probably has strict port filtering and 89 cannot pass though.
If anyone asks "how are you're doing that" just blame the 3G connectivity.