To lookup a phone number with the Twilio CLI, you need a free Twilio account and the Twilio CLI installed in your terminal, followed by logging in with your account credentials. The API can perform two types of requests: carrier information and caller name identification. The Twilio Lookup API helps identify the carrier behind a phone number, which is essential for verifying real mobile numbers and detecting fake profiles used by scammers or spammers. The API returns a JSON response with information such as the carrier's name, line type, and telecom provider. While the carriers returned may not be accurate due to rebranding changes over time, Twilio is working with industry leaders to address spoofing issues, which are expected to be addressed by 2020.