Conference calling multiple iphones - max capacity

I understand that up to 5 calls can be merged at one time to create a conference call. Is it also possible for other iphone users on that same call to add callers to *their* call, thereby enabling a conference call for more than 5 participants? I need to get 8 people on the call. All of us have iphones, so wondering if I can merge 4 callers, and one of those 4 can also merge another 4 calls to get us to 8 lines.

Thanks