Sorry for the late response!
Tickets have been opened from both parties with the same response "not our problem". The users calling for my tests have been from personal cellphones by three out of state users who have their own separate plans. With that said, it is unknown as what number format some of our customers/prospects have. I can say, the direct lines share the 678-383-xxxx format.
In regards to forwarding, one phone is set to ring simultaneously with the user's cell phone and the other two do not forward or simultaneously ring. All three have the same issue and all three use AT&T for their cell phones, not Verizon.
Thanks ahead of time!