In order for Sideline to give you perfect voice quality, the app uses radio towers to transmit voice signals (same as your phone carrier) to make calls. For this purpose, you will need to register a phone number (VoIP RPN is not accepted) as a mandatory part of the account creation process.
Important: Only US-based phone numbers are accepted at this time.
If you don’t have a number, you may be interested in our other application, TextFree.
Please Note: Sideline is designed to be used as a second number for your mobile device and relies on your mobile service for managing communications. Therefore, you will need to use your Carrier cell phone number when registering for your account.
Using a Voice over Internet Protocol (VoIP) number, or a number not associated with your device will result in the inability to register for an account and an inferior experience as Sideline is not designed for that use case.
If you have further questions, please submit a request.