My experience with this is that voice quality on the line deteriorates with each additional party added. By the time you get to 6 or 7 people, it’s really hard to understand the conversation. Especially if more than one person starts talking at once.
I’ve done it with about 8 people for kicks. As the others have noted, you need one of the parties involved to be able to further connect you, and so on, indefinitely. Ofcourse, the more there are the greater the chaos.
However, my previous cell phone could support 6 people in a conference call directly. So more than 3 people in a call without the need for additional people to have conferencing facilities is possible, although your bell south line will not support this.
Additionally, if you have a two-line phone, you can use the instrument’s conference button to conference the callers between the two lines.
So, suppose you have 2 bell south lines coming into the 2-line phone with conference button. You can call 2 people on line 1 using bell south’s conference facility. You can call 2 people on line 2 using bell south’s conference facility. Then you can press the instrument’s conference button and the 5 of you can talk away.