Your number never changes. You forward your existing church line to your agent, so everything you have already printed stays correct.
Nothing. It stays exactly as it is — on your sign, your bulletin, your website, and in every member's contacts. You never reprint a thing.
Here's how it works. When you set up your agent, you choose a local area code and the agent gets its own number in your community. Then you forward your existing church line to it through your carrier — AT&T, Comcast, whoever handles your account. It's a setting on your account, not a rewiring project, and we haven't yet found a carrier that won't do it.
Some churches flip it, and this is where it becomes a scheduling tool rather than a phone setting. Instead of forwarding the church line to the agent, they publish the agent's number and control where each call lands.
Say your office is staffed part-time on Tuesdays and Thursdays. In your organization settings, the availability schedule lets you decide when the agent answers and when it doesn't — a full day, or just a portion of one. Calls go to your staff member when she's in, and to the agent the rest of the week. Same number for the caller. Completely different destination depending on who's in the building.
You decide which approach fits your office. Both keep your number, and both keep you in control.