Can't Register SIP Phones after changing SIP Port

[genocide_hoax]

Hello,

I changed the sip port from 5060 to xxxx using sip.conf. after which I am not able to register any of my sip phone.
I also added the same port in my iptables using

iptables -A INPUT -p udp -m udp --dport xxxx -j ACCEPT

Still no luck. Please help me out with this.

Regards.