I have advised you to check caption call website, there is FAQ which already answered your question.
Will using CaptionCall increase my monthly phone service bill?
No. CaptionCall works automatically with your phone service provider, with no increase to your monthly bill. And because the captioning service is free and funded by the FCC, you won’t have to pay any additional monthly fees to use CaptionCall.
Does using CaptionCall impact the services I’ve selected from my phone service provider?
No. CaptionCall works seamlessly with the services you’ve selected from your provider, including call waiting, call forwarding, voice mail, and caller ID.
Can I use my CaptionCall Phone for long-distance calls?
Yes. Your phone service provider’s standard long-distance charges will apply.