# Phone Verification System Phone Verification System (PVS) is a WHMCS addon that helps eliminate fraud and makes sure accounts created are legit as each phone number is verified to make sure it is real. The system allows you to use four different API providers, [Nexmo](https://www.nexmo.com/), [Clickatell](https://www.clickatell.com/), [Twilio](https://www.twilio.com/) and [MessageBird](https://messagebird.com/en/), With the option of setting your verification API, and strategy. Alternatively, you can integrate any other SMS API provider using our new Custom Dev Kit. Clients who are in your WHMCS database before you enable the module, will not be effected and will not require to be verified. This module will only verify new clients. If required, you can also add old accounts to the module and get them to verify their phone number. **Proud to say that this module doesn't alter a single template file.** --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://layerlabs.gitbook.io/phone-verification-system/phone-verification-system.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.