Text messages and/or calls to or from Sideline will not show up on your phone bill.
However, you will see two numbers on your bill related to your Sideline account. These are called your pilot numbers. One number is for incoming calls and the other is for outgoing.
These numbers can be found in your device's address book & your call logs/history. Pilot numbers connect your incoming & outgoing Sideline calls through your carrier network, which is why these two numbers will be displayed on your phone bill when you use Sideline.
If you have any further questions, please submit a request.