Monthly. Your first bill is taken at checkout — it covers your first month of service.
After that, we charge your Zable credit card about 8 days before each new month starts. So if your next month starts on 12 September, we'll take the payment around 4 September.
See your bills in the Zable app: Zable Mobile → Manage plan shows your last bill, your next bill, and when it's due.
If you're keeping your existing number, your service starts about a day after checkout, once porting completes, but your first bill is still taken at checkout.