I think there would be too many variable to consider to implement an ISO standard to all telemarketing but it would make sense to break down the activities and assign them standards. I.e. Outbound B2B, Outbound B2C, Inbound B2C and Inbound B2B. For now it might look like a balance between list acquisition, telemarketing technologies, messaging, laws, telemarketing training, workflow, etc... I've built flow charts based on current client activity and worked through the processes of improving each area to where there is "maximum" efficiency. Until the day when it's laid out with clear statements there is as much art as there is science in creating a best practice environment.
On a side note...the words scam and illegal are sometimes exclusive. Outside of law there is a certain amount of interpretation and opinion as to what a scam is. I've purchased items and services that I was completely happy with that other may call a waste of time and money and having been sold under misrepresentation. We need to be careful what we consider a scam. Looking at client satisfaction and customer complain resolution need to be part of that evaluation process.