To stop telemarketing calls:

"Quiet mode" silences the ringer but accepts messages.
Search for "telephone quiet mode" on Amazon.
For example:

Do Not Call Registry

Do Not Call List - 888-382-1222

Bright House Telephone "No CallerID Blocking" -- *77
To Unblock (allow) -- *87
Century Link may require special order.

For Android Cell Phone:
Settings->Call->Call Reject->Reject Calls From->Private Numbers (Check on)
Call Logs->Long Press number to block->Block number

SENTRY Call Blocker. Block Junk and Robot Calls.