When BroadvoxDirect.com had Residential offerings, they would start the billing date based on the first minutes used. Either Call Forwarding, Received Call, or Placed Call. Still, when comparing VoIP providers, they seem to have been the one exception to the vast majority, and no longer offer Residential service.

When an account is created, there is the monthly expense of the reserved DID, and the activation of E911. They provide an initial money-back guarantee that eats that expense plus minutes used.

Vonage used to limit you to 200 minutes usage (I don't see it anymore in their TOS now) and if longer than 30 days, they charge an extra $39.95 termination fee, that is waived with return of the device, or if you owned it for 2 years or more.

In comparison, VOIPo is very generous in what they honor.
(Can't seem to find a link to the terms of 30 day guarantee ...)