I’ll be using sip phones with my asterisk box.
Now i want to configure my firewall (iptables).

Knowing that Sip protocol suffers with firewalls,
is there anything that i need to pay attention?


The answer depends entirely on your network configuration. You haven’t said anything about that. For a start, is the firewall running on the same box that Asterisk’s running on? If so, is that box directly connected to the internet? Dynamic or static IP? NAT?

The things to look out for are incoming ports - SIP (5060 is standard) and RTP (configured in rtp.conf). Also, externip and nat=yes in SIP.conf if you’re behind NAT - but not if you’re doing the NAT on the same box as Asterisk is running on.