Here’s the story :
I subscribed, few weeks ago, to an “unlimited data plan” from my mobile provider. I was so enthusiast that I sold my old Nokia N70 (Symbian OS8) on Ebay to buy an expensive Nokia E90 (OS9), infinitely more adequate for heavy use of www and networking applications.
I quiclky discovered “what’s under the hood” : this “unlimited” data plan is restricted to HTTP traffic on port 80 by use of proxy filtering that mean no IMAP, no POP, no VNC, nor TELNET… 
Moreover, there’s an extra filtering on User-Agent to (loosely) prevent its use from your computer by using the phone as modem for example.
I quickly had to found a solution, and the only one available was Tunneling, more precisely HTTP Tunneling, since writing Tun/Tap drivers on Symbian platforms is not possible without manufacturer’s SDK. After some Googling, I found the GNU HTTP Tunnel under GPL license.