Your card is charged at the start of each month for the plan you are on: $10 for 40 credits, $100 for 500, or $400 for 3,000. The first month is prorated. If you use more credits than the plan includes, the extra credits are billed at the end of the month at your plan’s rate: $0.25, $0.20 or $0.15 each. There is no setup fee and no contract.
What a credit buys. One credit is up to 60 seconds of call time to a US or Canadian number. Calls to other countries cost 1 to 6 credits a minute depending on the destination; the calculator on the pricing page gives the exact rate for any number. Dialling in to hear messages is free and uses no credits.
A rough sizing: fifteen one-credit alerts a month sit well inside the Basic plan’s forty. Callbacks are calls too and use credits like any other call, so on a phone with voicemail off, a message nobody acknowledges can cost more than one; the fix for that is to acknowledge, not a larger plan.