Some routers alter SIP packets with the default configurations which creates VoIP service problems. From your router’s web configuration page (usually under configuration / firewall / advanced settings);
- Disable Stateful Packet Inspection (SPI) if applicable.
- Disable SIP Application Layer Gateway (SIP ALG) if applicable.
Try disabling your firewall (turn it off completely) briefly. Reboot your router and VoIP device and check if you can make/receive calls. If you can do so now then your problem was with your routers firewall configuration. You firewall is not allowing calls to your SIP phone. You can continue using your router as firewall disabled or if you want the firewall enabled on your router try following solutions.
Port 5060-5061 for UDP and TCP
Port 16384-65535 for UDP