Phone Number Scrubbing
Phone number scrubbing cleans your list of data and checks the phone numbers on the list for: fake numbers, landlines, inactive numbers, numbers on a DNC list, etc. This will help you with your deliverability and sending reputation.
Recommended Company: https://www.datazapp.com/phone-scrub
Cost: 0.005c/phone number. ($10 gets you about 2000 phone numbers scrubbed)