You could use a payment processor and also a call system such as twilio. If you want to work with the phone companies (i.e. 1900 number in the US) this is also an option but the API's are not friendly (or non-existent) and they will take a larger fee.

Here are the key steps to starting a chat hotline where callers pay by the minute or at a flat rate:

1. Get the necessary telecommunications licenses and registrations for offering a paid chat or call service. Requirements vary by country or state, but you'll likely need some form of authorization.

2. Choose your calling or chat platform. Popular options include CallHippo, Talkroute, Sinch, Twilio, Voxbone, etc. These platforms allow you to set up toll-free or premium rate numbers and assign costs per minute or flat call rates.

3. Purchase toll-free or premium-rate phone numbers from your chosen platform. Numbers starting with 800, 888, or 900 are typically toll-free or premium.

4. Set up your call/chat flow and menus using the configuration tools on your platform. Define greetings, IVR options, call queues, etc.

5. Integrate billing and payments. The platform should have options to charge callers automatically based on call duration or a flat fee. You'll need to settle payments.

6. Market your hotline service. Promote your toll-free number across websites, ads, etc. Clearly state the per-minute rates or flat fees.

7. Hire and train chat agents. Have live agents answer calls during business hours to provide the paid service.

8. Monitor call analytics. Track metrics like call volume, duration, and revenue to optimize the service based on user behavior.

9. Consider additional features like voicemail, call recording, and CRM integration for a better user experience.

Start with a simple setup and refine it over time based on customer feedback. Ensure all legal and compliance needs are met before launching a paid chat hotline service.