You can now change your Envoke subscription plan on your own any time from the user interface.
Go to the Billing Details page under the My Account tab and click the “Change plan” or “Upgrade account” link.
Each new subscription you select is a monthly plan paid by credit card.
When you switch to a new plan you will not lose your existing email credit balance – emails included in the new plan will be added to it when your subscription plan changes. For example if you have 3,500 email credits and upgrade to the 15,000 emails/month plan, your new balance will be 18,500.