It seems that there are some conflicting points of view, and perhaps some ambiguity regarding what voipo actually uses and requires.

Perhaps a moderator can chime in and clarify if TCP or UDP is preferred for SIP?

Also, I have definitely had to disable SIP/ALG on numerous installs, and I recommend doing it if you have any connectivity or audio issues.

On the other hand, I've done hundreds of installs, and never had to disable SPI, let alone an entire firewall. SPI implementations should not affect packets for active connections... only for unknown packets. So I would say that disabling SPI is a last resort and not something you should necessarily do at square one. In fact, turning it off could leave your network vulnerable to flood or denial of service attacks. These attacks aren't common, but are on the rise. So just because I haven't experienced it myself, doesn't mean it is safe to assume no one will experience such an attack.

My own approach is to make only the minimum necessary changes to allow connectivity and audio traffic. And disabling one's firewall entirely, in my opinion, is not sound advise. Your mileage may vary.

Good luck to all, have a great Christmas, and a Happy New Year!