In July 2015, the Federal Communications Commission issued a Declaratory Ruling clarifying how they would consider whether a marketer complies with the TCPA law when making calls.
This is the summary for non-lawyers prepared by a non-lawyer.
System must dial one person at a time, and not more
System must not allow a user to abandon more than 3% of the calls
System must handle busy, disconnected or no answer calls with brief intervention from the agent
The agent is actively involved before initiating every call
Triple line dialing
Dialers that hang up on answered calls
Any dialing platform that can dial thousands of numbers quickly
Ring.io's List Dialer is not an auto-dialer and is designed to comply with the FCC TCPA ruling.
For more details on the ruling, you can refer to this excellent summary prepared by the law firm Allen, Mitchel & Allen.