Firewall is off but connections are still blocked?

On iChat I've had some problems. I can message anyone but I can't call anybody. When I call them it waits for a response for about a minute and then tells me the call was rejected. When I googled to find the answer I came up with alot of people saying the firewall had to be blocking yada yada yada. Well my firewall was off so I moved on to the next answer and tried alot of things to make it work. Well fast forward about a week and I decided I was going to turn my firewall on and then open communications for iChat. Guess what... that worked. Suddenly I can call my friends again. Then I turn the firewall off and I can still call my friends. While I am extremely happy that I have figured out the problem... the problem in and of itself doesn't make any sense. If my firewall is off then iChat's connections shouldn't have been blocked. I had Snow Leopard on this computer originally but I never used iChat so I can't tell you if the problem originated there. I've recently upgraded to Lion and when I did that I also moved from Skype to iChat (Microsoft buys Skype and now support for Mac's Skype goes down the drain... go figure) so I didn't notice the problem until I was on Lion. I have a 2.4 GHz Intel core 2 Duo MacBook from mid-2010.