I’ve read that the S700 support 5-way conferencing. Is there a specific way this needs to be done. If I’m in a call and conference a third person, hitting the conference will not allow me to dial a 4th or 5th person.
Your extension probably has a limit of 3 channels. Try increasing the limit.
(I’m actually not sure how conferencing on the Sangoma phone works, perhaps it doesn’t actually use separate channels?)