My mobile company offers a free package for facebook with unlimited bandwidth , however when I open my 3G connection the mobile automatically connects to unknown servers (maybe google) and the mobile company charges me for that connection.
The question in simple words:
How can I make all connections blocked (even google) except facebook.com?
If you're rooted, you can configure Firewall rules to block all except Facebook, but I don't think your problem is that complex:
when I open my 3G connection the mobile automatically connects to unknown servers.
Unable to understand what that mean as I can't OPEN my 3G connection. Seems to me, either you are talking about opening web browser or Background Data is screwing you. In the first case, make your homepage Facebook. In the second case, turn off Background Data from Settings ~> Accounts and Sync. Done!
If you want to do it with Firewall way, open Terminal Emulator. Switch to root by su command (your device must be rooted for that). Now, execute following commands in sequence:
iptables -A OUTPUT -p tcp -d facebook.com -j ALLOW
iptables -A OUTPUT -p tcp -d * -j DROP
(Do it on your own risk after proper backups. Some devices become unstable after it.)
