Your Results are: You should choose a premise solution
You said that there are regulatory and/or compliance requirements for you to own and/or maintain full control over your data. Your communication and collaboration tools contain considerable amounts of data, including conversations via chat or instant messaging, call recordings, voice mail messages, and more. To maintain control, a premise solution is a better choice for you. A private cloud solution may provide the control you require; this option will require investigation and due diligence.