** Spam calls and robocalls are a significant issue for high-volume customer service centers, impacting their bottom line. The Twilio Marketplace offers third-party technologies to integrate with the Twilio API, such as Marchex Clean Call, Nomorobo Spam Score, and Whitepages Bad Reputation. These Add-ons can be integrated into the Twilio Console and used in C# code to block spam callers, robocallers, and scammers. The code checks the spam score of the number and handles the call differently depending on whether the Add-on considers the caller to be a spammer or not. The `IsBlockedByNomorobo`, `IsBlockedByWhitepages`, and `IsBlockedByMarchex` methods handle the data from each Add-on, returning a `<Reject>` TwiML tag to send spammers packing or a `<Say>` TwiML tag to welcome legit callers. The code is flexible and can be modified to handle missing data in the JSON response. To test the blocked call, unit tests can be written with dummied up JSON to ensure the call goes through as expected.