If you have an E61 and upgraded it to latest firmware so you could use VoIP behind firewall. You have discovered that it ain’t so easy as there is no manual setting for firewall traversing. Do not throw your phone at that wall yet!

NAT traversing is only settable by remote provisioning ( you need a server, send some SMS messages and so on ) or…

Using plugins as they call them on www.forum.nokia.com, it is very fortunate that Gizmo VoIP has already produced one. If you use their service it’s perfect for you. If you don’t ,still helps.

Simply go to their website, download plugin, install it to your phone ( I have downloaded it using build in browser in E61 ) and run, it will ask you for your gizmo login detail, put some rubbish, and finish. Then go to your Settings , locate Gizmos SIP Profile and modify it so it will use you prefered  provider details and bang it works 🙂

enjoy