How do I test a firewall?

How do I test my consumer grade network to know that SIP calls are working inbound and outbound, that there’s no problem with firewalls at any level? At this point I just want to establish that SIP calls can be made to the wider internet as well as within the localnet.

for this router:

Hardware Version WNR1000v2 
Firmware VersionV1.1.2.54NA 
GUI Language VersionV1.0.0.110 
Operation ModeRouter 
LAN Port 
MAC Address <omitted>
IP Address192.168.1.1 

DHCP Server On

MAC Address <omitted>
IP Address <omitted> 
Connection DHCP 
IP Subnet Mask
Domain Name Server

Because an Ekiga SIP account can call a getonsip SIP account, on different physical devices, across the LAN, it certainly seems that there are no firewall issues.

You need to test also dialing to outside, to make sure all is working fine. Nat Issues could cause one way audio or no audio and call cut off before or after 60 seconds

Currently, I just have a SIP account, no trunking or DID configured. Once I have a DID configured, how would I go about testing? Tools like sipsak and sipp?

Are there tests I can run now to establish that everything is working fine, without a DID?